MGB Interior Panels - Part 1

I spent a great deal of time working on Zed's body. Before and after that, I spent even more time on Hapy, with the wiring (both the re-wire and the P0121 code), the furnace and the heater. Around those efforts, I picked up and improved upon T's old Audi, Nemo. Today, I took a break from those other cars to return to Oliver, the 1978 MGB, to complete some interior things I had left undone. I was going to get after Nemo's rear wheel bearings, but honestly, I just want something in the warm garage and Oliver is the only car in a garage, so... off we go into another multi-part post.

Where Were We

Recall that I blew some manna-from-heaven on an interior refresh for Oliver two years ago (See New Seat, What a Treat Parts 1, 2, 3 and headrests). I completely restored his seats, replacing all of the foam and the covers. Out with the old black vinyl and in with new cream with black piping leather. The lighter color is really nice when the sun is super intense, like in the early Summer here. I put in seat-heating elements, but haven't wired them in yet. Instead, I focused on summer-supporting stuff, like the new stereo. This new stereo included front speakers attached to contoured plastic boxes mounted to the outer footwell sidewall (See MGB Gets Sound, Version 2), but the kick panels were not there, so I started with those.

Kick Panels

creating kick-panel pattern

The kick panels compliment the seats in that they are the same cream color. When I ordered these, I appear to have selected the option to include map pockets, which I guess are okay, but with the little speaker boxes, will not be terribly useful. Anyway, in order to pierce the kick panels in the exact right spot so I can mount the speaker boxes, I pulled a paper shopping bag and some cardboard out of the recycling. I traced the kick panel onto the paper and cut out the pattern. I removed the speaker box from the driver-side sidewall, set the paper against in it's place and found the mounting holes with a small nail. I transferred the holes onto cardboard to test the location, and they were a little off. So, I pushed the nails around until they were in the holes well and tried again. They were still a little off, but the third time they were perfect. I transferred the holes onto the rear of the kick panel and drove the nails through from behind with a framing hammer. I set the soft cream material onto a shop towel and set that on top of an old kitchen cabinet door so the nail could pierce without damaging the panel.

speaker box
attached to p-side panel

After presenting the speaker box to the panel, and pressing the mounting screws into their respective holes, I drove the screws into the panel and then held the pair against the side of the car. I needed to position the panel around things, so this actually happened more along the lines of... in, then out, then in then out a few times until the panel was tight against the leading edge of the door weather stripping, the holes were aligned and the screws were lightly threaded in. I verified the routing of the speaker wire and then set the screws all the way in into the speaker box was snug, but not overly compressing the panel. I re-mounted the speaker and turned to the passenger side. I followed was the same process, down to the multiple sheets of cardboard. Since there are fewer obstacles on the passenger side, it was easier, but only barely because I did the whole thing leaning across the transmission tunnel from the driver seat. I could still feel my ribs 2 days later, but they really look good. Pain is temporary; beautiful clean kick panels... well, they're kind of temporary too. Just not quite as temporary, I hope.

Rear Quarters

With the kick panels in, the door panels look that much more black. And wrong. So, I really needed to keep going, but I thought I would do the doors themselves last. There are 2 triangular-ish panels that sit just aft of the seats with the rear-most edge following the contour of the front of the rear tire well. So, I call these quarter panels; I'm sure they have another name, though. I thought they would be easier than the door cards, and with the location of the car so close to the wall on the passenger side, I'm not sure how I will get to the passenger door anyway.

ideal top orientation
to hit all 3 bolt heads

These need to fit under the convertible top mounts, but otherwise their positioning is fairly straightforward. The 3 bolt/screws are partially obstructed by the convertible top frame. So you cannot just lower the convertible top to remove the 3 bolts that hold the mount to the car. You can remove one, but to get to the other 2, the top needs to be partly open. This is where an extra hand is very helpful. I didn't have one, so I tried doing just the driver side first. I started by opening the top so it was sticking almost straight up. This exposed or unobstructed all 3 bolt heads.

When I removed the the rear-most bolt/screw on the driver side, the capture-nut inside the B-pillar fell off (30 year old weld failed). Also, one of the hinge-points on the passenger-side of my convertible top frame separated. The capture nut is easy: they are sold on Moss for around $18US. For the hinge-split, I literally held the pin where it was supposed to go and forced the pieces back together with channel-lock pliers. I looked around for repair kits or something, but I was unable to find anything. At this point, though, it is working.

To get a sense of the work, I did complete both sides (using only 2 screws/bolts on the driver side), one at a time, leaving the other side firmly attached. With the convertible top frame up, just like it is pictured above, remove the 3 bolts/screws. I completely removed one, and then moved back and forth on the other two, slowly removing them. With the frame lightly held in place, I shifted focus onto the panels.

 

The Doing

I tried 2 different approaches, and found the second approach works better. First, I tried to poke a tiny hole in the panel for each of the 3 bolts to pass through and then widened the hole with something so the screw/bolt can thread in without catching vinyl/leather on its way. Take care not to make it so large, however, that it is larger than the frame hole supports. On the passenger side, I used a razor knife to cut a small "X" for each of the 3 holes. Either way, set the panel nearby, and get yourself seated on the parcel shelf at the rear of the passenger area.

I completed the removing of the 2 final bolts while holding the frame steady with my head. Yeah, that's right. This is where having a helper would be very helpful. With the frame held steady (either with your head or by a helper), lift the mount up just enough to get the card in place. I set the rear-most corner in first, and then flexed the card to press the leading edge behind the weatherstripping. The holes for the frame will line right up, but I checked with a bolt to make sure first. Then, I lowered the frame down into place (optional tonneau cover mount held firmly against the top frame), and sent a bolt through, threading into the nut. With one fingered in, I sent the other two in, and then moved from bolt to bolt until they were all snug.

At this point, I have both of the front panels and both of the rear panels in. The doors are a little more complicated since the glass-scrapers need to be replaced, and the old cards are still in. Since the weather around here has been below freezing and wet (ice, freezing rain, sleet and snow), I will be continuing to play with Oliver since he is in the semi-heated garage until the weather changes.This means that my next post will probably include some work on the driver-side door card. The passenger side is trapped against a shelving unit, so I probably will not be getting to it for a while.

 

As always, thanks for following along-

MGB Battery Monitoring

Sometimes, when you're working on one thing, it is a really good idea to take your mind off of it by working a little bit on something else. Today's post covers my distraction from Hapy's electrical issues.... with the battery issues on Oliver (the 1978 MGB). LOL. For my local-to-the-Pacific-Northwest friends, I hope you have heat and power. I know some friends have been without both since Friday. Grateful we are finally above freezing.

Flat Battery

Our saga begins with Oliver's battery going flat from being parked for a few weeks. I first noticed it in early fall after parking him in the garage for the winter and forgot to hook up the float charger. When discovered, I put the battery on the float charger like when it was parked outside, but wanted to know the root cause. I started with swapping out the battery for the battery we had pulled from donor Zed. That was a good battery that still held 12.5V almost a year after pulling it out of the donor. It barely fits in the battery box, but it would run flat if left off the float charger when hooked up to Oliver's battery cables. I decided there was something pulling vampire amps off the battery.

Clock

original oil temp
and clock look

I am sure there are faster, more scientific ways to figure this out, but this is what I did: I pulled all the fuses, and put the battery cables back on the battery. I left it like that for a week and found that the battery did not run flat. This told me that the drain wasn't from some ShadeTree wiring that did not run through the fuse-box. Then, I checked the amp draw across the fuse pins, and found that the draw from the bottom-most fuse registered on the meter. That fuse provides power to the interior lights, the trunk light and the clock. These old analog clocks consume much more power than their digital counterparts, because they need to run little motors that turn gears rather than a tiny computer to keep the time. I decided I would pull the clock and put in a gauge that might be more useful: a volt-meter.

 

This removal is interesting. The VDO gauges with which I am most familiar have a threaded collar that goes all the way around the base of the gauge. You push the gauge through the hole in your dash and then thread on the collar from behind. These original MGB gauges are not like that. Instead, there is a cross bar that is shaped like a "U" with a hole through the very center of it. That hole aligns with a threaded stud exiting the center front (again, front is front) of the gauge. Once the stud passes through the hole, the ends of the "U" press against the dash, and a nut is threaded on to hold it in place. While more elegant, it is actually harder to manage with 2 hands. Otherwise, I think it is the better mount because you can wire your gauge while it is dangling through the hole in your dash, test it and then mount it without disturbing the wiring. With the VDO mount style, you need to either be optimistic and run the wires through the collar suspended behind the dash -OR- do that after you have tested.

Volt Meter

volt-meter installed

The gauges in the old MGB were made by a company called "Smith". So, if you want your gauges to look authentic, it is best to buy Smith gauges. Here in the US, that is quite difficult to do in-person or at least within the borders. Enter eBayUK. I found someone selling off a perfectly good voltmeter that was era-correct from a different British car. It cost about $100US delivered, and it arrived faster than some other things I have gotten from the east coast. The wiring is quite simple. there is a ground protruding from the front (front-is-front) corresponding to the far bottom end of the voltage scale. On the other side, opposite the top-end of the voltage scale is the signal input. In-between is a tube into which a bulb is set. This requires the bayonette-style bulb similar to the clock, and the other gauges in the MGB. I just reused the one from the clock.

Testing

Of course, I could not just pull the clock and slap the voltmeter in without some tests. First, I wanted to see how/if it worked. So, I ran a wire from the negative post on the old MGB battery (sitting on the garage floor on a float charger). To the positive post, I ran a fused wire (wire to a fuse to another wire) to the supply-side of the voltmeter. The needle slowly moved up and settled just below 13V. Perfect.

 

Next, I grabbed the clock I had removed. I confirmed that the clock would run using the same test wiring set up first. Then, between the fused wire and the supply side of the clock, I ran my meter to see what the amp draw is. On the second to most sensitive setting... or is it least sensitive.. setting, I got an amp draw: 30. Interesting. I did the same thing on the voltmeter and got 3. So, the clock draws 10x as much juice from the battery as the voltmeter does. I figured that the voltmeter, even if it was on all the time, would allow the battery to hold a start-able charge 10 times longer. So, I decided that running the voltmeter to a switched source was not necessary. I may revisit that one day, but for now, I figure that I can look into the window of the car and see if we can go for a drive. More importantly, I could simply re-use the wires that I had just removed from the clock.

Install

volt-meter test with 
running lights on

Installing the voltmeter was quite easy. I plugged the red/white wire into the light bulb I scavenged from the clock. I plugged the black ground wire into the ground and the purple wire that used to run the clock into the voltmeter sensor plug. I confirmed the wiring by putting the battery cable back on. Yes, I could have done something with less potential for failure, but I would have had to do something like this eventually, and it was only 3 wires. I wrapped the end of the purple wire with electrical tape so I didn't accidentally short the circuit (and pop that fuse). Then, I set the gauge into the hole, put on the "U" with the arms touching the dash such that they were not anywhere near the supply side (running approximately from 1:30 to 7:30 on a clock-face). A quick thread-on of the retaining nut and it's in.

Between the weather and the pile of non-operational cars in the driveway, I cannot take Oliver out to test the gauge. But, since I hooked it into the always-hot circuit for the interior lights, I can verify that it works simply by looking at it. It currently reads just under 13V. So, we're good. I intend to leave the battery hooked up without a float charger and I will be checking the battery condition every couple of days. If the voltage drops enough for me to notice (or below 12V), I will put the float charger back on. at that point, I may search additional vampires. At this point, I think I slayed the one that was draining the battery.

That's it for today. Thanks, as always, for following along--

Hapy Daily Driving

Well, that title might be overstating it a little bit. To clarify: Hapy is now capable of driving on a moment's notice. With the CoViD safer-at-home, I haven't been going anywhere. I may not have had an operable car for most of the last couple of months, but the lockdown has meant I haven't really needed one either. Today, I'll cover the little things that needed to be buttoned up after the big re-wire.

Reverse Lights

I mentioned the reverse lights at the end of the Electrical Gremlins saga. I had it wired up to a somewhat mystery switched 12V source before. When I tore the old wiring rats nest apart, it was left out of the new wiring. This resolution was fairly easy. Back when I set the mystery wire-up aside, I left the plastic-snap-shut fused wire in tact. So, there was just a plain bare wire to deal with. I fished it up into the spare tire well / wiring compartment from the engine bay. I spliced the wire into the switched source splice coming from relay 109 so the reverse lights will only come on when the computer thinks we are in "RUN". Since it already had an integrated fuse, this was a simple splice effort.

Headlight Flasher

When I was chasing the cause for my lack of amps during P0121 testing, I tore into the dash. I thought I had bumped something loose, and there are a bunch of things in there that could have shaken apart. Well, I didn't bump anything loose causing that issue, but I did bump something during that exploratory. Haha. During the Summer of 2020, I finally got my high-beam / low-beam flasher relay to work. It was because the replacement relay requires a source of 12V to pin 30. This pin wasn't on the old relay, and there is no wire leading to that pin in the original fuse box. I solved that before, but when I was looking for the buzzing noise during the P0121 effort, I pulled that relay and the wire heading to that pin fell out of the fuse box. I didn't notice that then. During post-testing, I discovered that the flasher no longer flashed. I found the wire, re-oriented it so it would not fall out, and returned things back to their prior cleaned-up state (zip-tied fuse-box). Hi-beam flash/relay works.

Defroster

Also in the Summer of 2020, I installed a defroster. Sort of. The defroster solution was moving the Vanagon rear heater under the belly, routing coolant along the driver side main beam and plumbing into the old air channel from just behind the front crossbeam. The air source was an experiment pulling from the old rear floor vent. The mechanical connection of the hoses to the heater was poor, and the experiment fell apart. This source needed to be remedied. Also, the switch was not operating the fan settings correctly. This was caused by poor quality wire connectors, so once the 3 at the switch and the 2 near the heater were replaced, we have a 3 speed fan again.

I decided that rather than solve for a cabin-source of air for the defroster, I would just remove the experiment for now. I have an idea for a source, but other cars need my focus. So, I removed the air supply hoses and called it good enough for now.

Mop Up

During all of the wiring work, the inside of the bus became considerably disheveled. It was one part shed, one part tool box and no part looking like a vehicle. This was easy to resolve, but made a huge difference in declaring the end of the work. The lot couch is back installed as a middle-row bench seat, for example. The rear speakers are hooked up and placed for sound again. After a quick trip with the shop-vac to get the wire-strippings and other fallout from all the work vacuumed up, he looked nearly ready.

I ran a test of the furnace, confirming that it would run on either the accessory battery or the main. It will, but the current draw for the glow-plug is so significant that I'm not sure I will want to start that heater if I am not running at least a float charger to the sourcing battery. Still, it moved the internal temperature of the bus from 43*F to 68*F (6*C to 20*C) in about 15 minutes. For the fuel-minded, it took about 500ml (or ~0.13US gallons or about 2 cups). As I understand it, maintaining the temperature requires far less fuel, so the consumption at that point dropped way off. I left it running for about an hour and the total consumed ml was about 530ml or 30ml (1/8 cup) for the remaining 45 minutes of keeping the bus warm.

I took one last step: I installed plastic kick panels I ordered like a year ago against the rear of the nose of the bus. Just like that, the cab looks like it is not an active project. It looks fairly clean now, actually. They install and remove easily, and once snapped in they really do not appear to need much more to hold them in place. The guy who makes them suggests poking holes through and screwing them into your bus. I might use Velcro, but I'll withhold decision-making until after we have had a few drives to see if they rattle or not.

Getting Legal

This last thing was actually one of the first things I did for Hapy after I set Zed aside. In fact, I think it was the registration that got me thinking about Hapy in the first place. His registration came due, and because of CoViD-19, I had to do it remotely. Since he is too old for smog and Oregon does not have inspections, I have been renewing his registration online for a few years. Still, this time I did the online steps in October 2020, but did not receive the stickers for his tag until January 2021. This used to take a couple of weeks at most. It sure felt good getting those stickers on his plates, though.

Test Drive

With the tags updated, the wiring fresh, the defroster responding, furnace functioning, etc... Hapy appeared nearly ready to be pressed into service. We just needed a test drive. For that, I did my usual neighborhood lap through a series of side streets out to the main drag, a quick 1-mile straight shot on that major street and then turning back into the side streets for home. As expected, Hapy was fairly peppy and responsive. He sounds great, and did not suffer any P0121 issues. There were a few stutters, but no codes, so I chalked that up to old diesel. That will solve with some snake oil and a fill-up. Considering that Hapy had not left the driveway in over a year, this drive was significant, albeit short.

Alt-Light

The battery light came on when the engine was revving low during the test drive, leading me to think that the unsettling "pop" noise I heard when the wiring was wrong (See Chasing the Hapy Electrical Gremlins - Part 6) was the sound of my alternator frying. This light had been popping on during testing, so the fact that it returned during the road-test honestly just reminded me. Before I jumped into anything, I in-bus tested the alternator: I alligator-clipped a fused wire to the alternator output and ran that wire on the ground up to the cab. There, I electrical-taped the bare wire to the positive probe of my multi-meter to free a hand. I set the negative probe into a small bolt-hole in the driver door frame for a good ground. First, a good base reading: 13.5V. Cool. I started the engine and it dropped down to 12.4V. Solid. With my hand on the go pedal, I revved the engine and watched the voltage climb up and down peaking above 14V. So, the alternator is fine. Since I have been running without an ALT/GEN light for 10 years, I could just ignore that light... Nah, I just can't do that. I figured that the bulb must simply be connected to the wrong wire of the 2 in the ALT plug.

I had spliced into the wire heading to the computer (DFM - or Digital Field Monitoring), and it needs to hit the one that routes to the cluster (L - Lamp). Simple fix: I cut the splice from the donor main harness to the 6-wire cable, and tied it into the other wire from the plug just upstream from the 4-pin plug. While I was back there, I added ring terminals to the sensor wires for the oil pressure and oil idiot light. There remains some wiring tidying I need to do on the driver's side, so I'll cut out the rest of the DFM-sourcing wire when I'm in there. 

As much as I'd like to say that once I completed, I took another test drive... I can't. I did test start and engine-rev in-place, however, just to see that ALT light wink out (which it did). Why did I not drive him? Well, remember Gramps (1996 VW Jetta 2-dot-slow from my folks that we gave to K2)? He re-appeared with a failed throw-out bearing after the first test drive, but before I'd solved the ALT light. So, I will have to juggle the herd to get Hapy free for a drive. And, you can probably guess what I'll be working on next.

That's it for today. While I may not need to go out much due to CoViD restrictions, I now have my beloved turbo-diesel powered microbus available-ish for whenever the need arises. While there are lots of little things I could tweak on Hapy, none of those things would prevent me from taking a drive. Sweet, sweet success. Thanks, as always, for following along.

P0121 - the 1200 rpm limp mode - Final

Today I complete the saga of trying to resolve the P0121 error that persisted after I re-wired the front-to-back cable, the fuse box (main donor) harness and the fuse box / relay box. It is terribly ironic that this post arrives on Groundhogs Day. I have had drive-by-wire (P0121) issues so much since I did this conversion, it was like my own personal Groundhogs Day every time I dropped into that 1200 rpm zone. Queue the Sonny and Cher song. With only one error code, you would think this would have been easy. Nope. At least, after all the wiring changes, I only had the one code.

Pedal Pedal

new on bottom

When I left off my last post, I had concluded that the wiring was not the issue, and ordered a replacement pedal. These aren't cheap, but I found one for around $100US (which was a really good price). It took a while to get here from the east coast, but once in-hand, I thought it would be interesting to compare the new and the old. Physically, they are very similar, but the old one has a removable panel. I pulled out the multi-meter and started testing the resistance between all of the pins on both pedals. This was illuminating.

Then, I popped each pedal into a bench vice so I could depress the pedal by tightening the vice. This allowed me to measure how the resistance changed across the pins as the pedal was depressed. Generally, both pedals demonstrated the same direction of resistance change relative to the direction of the pedal movement, but there were some definite differences. For example, the resting resistance between the pins (which had a corresponding resistance on the other pedal) was lower on the old pedal than the new one. I was able to correct for most of the difference by shifting the little cover on the old pedal forward (front-is-front / away from the footpad). Prior to moving the cover, it was near the mid-point of the front-to-back adjustability.

The biggest difference I found was that on the new pedal, there was infinite resistance between pins 2 and 4 when the pedal was 0% depressed. The old pedal, however, had a measurable resistance (1760 on the second-to-highest sensitivity). Once the new pedal moved even a little off of 0% depressed, resistance was measurable. I thought this was the big tell that the old pedal was the cause, but before I get into the in-situ test, here are some tables and notes around my testing of the 2 pedals. I suspect there will be readers who are only here for that.

Testing Static Resistance between Pins 

inside the removable
cover

In the table below, the multi-meter was set at the second-to-most sensitive resistance measuring. The number on the top is from the new pedal, and the number below it is from the old one before I tweaked the little cover position. 

The word "flash" means that even though I tested these pin resistances 5 or 6 times, on the new pedal, the resistance between these pins would flash a quick 4-digit number and then go to infinity. I tried to measure it with different settings on the multi-meter, but for my purposes, it was clearly very different from the "old" pedal. Since it happened every time, I concluded it was not caused by my probe accidentally touching pin 3 while approaching pin 4. I did experience intermittent issues with my cheap $5US Harbor Freight multi-meter where the whole plastic probe would fall off the lead. The multiple tests ruled that out as a cause for the "flash" as well.

The "fix" for the probe-fall-off: Strip back a little bit extra off the end of the probe wire and push it back into the probe. Check continuity between the probes. Down to 0 or nearly 0? Perfect. Hold the wire and probe steady and tape the wire to the probe, and then run more tape up the wire a couple of inches. That wire won't pop out easily again.

Where were we? Oh, yeah.. while there are 6 pins, there was not a measurable resistance between most of them. That is why some pins are not on the tables at all and some pin intersections have a blank square. In both cases, there was no measurable resistance. Pin 1, for example, had no measurable resistance to any other pin. Neat, eh?

	3	4	6
2	1320 900	flash 1760
3		1010 996
5			1070 945

 

Testing Transient Resistance between Pins

Next, let's look at the throttle testing in the vice. So, consider these values as "when the pedal is depressed, the resistance between the pins..."

hunting gremlin

	3	4	6
2	unchanged unchanged	*drops (1590, 1480) drops (1570)
3		rises (1422, 1700) rises (1300)
5			infinite infinite

The * is to show that the resistance between the pins suddenly changes from infinite to something (high) 4-digit measurable once the pedal is starting to get depressed. The resistance between pins 5 and 6 goes to infinite as soon as the pedal starts being depressed. This is all really cool stuff, but are we closer to having an accelerator pedal again? Well, I plugged the 6-pin flat-connector into new pedal and started the engine. Idle... and then 1200 rpm mode. So, nope. So, next I checked the voltage of the 6 pins on the flat connector, and put my findings in another table below. Perhaps this would have been a good thing to test while waiting for the pedal to arrive. Or better yet checking before ordering one. Hindsight is great.

Voltage at the Flat Connector

The "should be" column is from comment #7 on this posting on the TDIClub. Fred's TDIClub is such a fantastic resource. Highly recommend for the knowledge, and they are generally nice folks too, unlike some other boards where so many replies to questions are "use the search function". Helping not helping.

	should be	no key	key to run
1	0-90%: 9+V	no V not ground	..8V
2	5v	no V not ground	5V
3	ground	ground	ground
4	.35V -> 4.5V	no V not ground	2.7V
5	0%: 0V >0%: 2.758V	no V not ground	8V
6	ground	ground	ground

So, I looked at this table and some of the values look spot-on, like the 5V reference voltage on pin 2 and the grounds on 3 and 6. The other 3 look like I wired them incorrectly. Like, maybe wire 5 should be going to pin 1, wire 1 to pin 4 and wire 4 to pin 5. At least then the voltages would be in the right ballpark. So, before I assume that my ECU is fried (the only other reason I can come up with for this), I decided to change some of the wiring to reflect this re-arrange first. Considering the difficulty I had determining the logic at the blue T10 I mentioned in the last post, this felt very much like a real possible cause.

Change 3 Wires

more hunting gremlin

Since the wiring on the fuse-box / relay-box harness was very hard to get to, and the 6-pin flat-connector is very easy to get to, I decided to change the wiring at the 6-pin flat-connector. This will force an update to my wiring diagram, but this was the fastest route to testing the theory while minimizing the potential "bump risk" (you bump something and now you have a whole new set of problems). Anyway, this re-wire was very easy: label the 3 wires, cut the heat-shrink, unwire, re-wire, re-heat-shrink.

Of course, any final test couldn't be without it's own challenges, as the electrical acted batty for about a day while I chased gremlins again. Something was creating a vibe, making the system act like the battery was dead. For example, the hazard switch would cause the relay to buzz, lights wouldn't come on, etc but a voltage test on the battery was fine. After several hours of tearing the dash board apart, believing I had bumped something when doing the flat-connector, I removed the battery from the bus and verified it had over 13.5V (full charge). So, I put the battery on the bumper and hooked up the battery cables, omitting the float charger, and tried the hazard. Success. Then I turned the key to run and everything acted normal. Love you, Hapy. Root cause: current owner error not tightening the positive battery cable on the battery post after changing the wiring. Sigh, sometimes are better than some times.

I pulled the positive cable off the battery and re-assembled the dash. While I was there, I cleaned all of the fuses and their connections with rubbing alcohol, and then zip-tied the fuse box up out of the way (it has never been screwed to the bus since I bought it). With the front-end cleaned up, I put the positive cable back on the battery (still sitting on the bumper) and checked again that things were normal. With the key turned to run, I checked the voltages on the flat-connector, and now the pins aligned with the table above.

Test Fire

battery on "bumper"

Feeling confident, I turned off the key, plugged in the new accelerator pedal and test fired the bus. Engine started, sat at idle, threw no codes... and working the pedal with my hands revved the engine. Hazah! To complete the loop, I removed the battery cables from the battery, and put the battery back in the bus. While I was there, I resolved some wire routing, and implemented a battery strap-down with the webbing I used to hold the speaker box in the MGB trunk (See Speaker Box Install Finish). This also is holding the battery-top fuse-box on top of the battery. I returned the battery cables to the battery posts (this time tightening them down) and did another test fire. Start, run and rev. With all the wiring and cables now sorted, I was able to re-install the original engine hatch prop, which means no more holding it open with either my head or a stick (like in the picture on the right, here, you can see a stick all the way to the left). More winning. And, of course, I bolted the pedal to the support post and tested the foot feel before heading inside for a celebratory smoothie.

The next day, I set out re-test the old pedal to see if that small resistance difference between pins 2 and 4 was meaningful. It isn't. The old pedal works correctly now, just like the new one: no codes, engine rev's. Since the new pedal is bolted in, I decided to leave it, and put the old pedal into my parts bin. In the end, the sporadic P0121 error that Hapy and I have suffered for the last few years was ultimately caused by something in the wiring that I replaced with the front-to-back cable at the start of the Chasing Electrical Gremlins saga (See part 1). Still, I will be putting the old pedal in a large Ziplock baggie under the rock-n-roll bed in case this new pedal fails on the road. So, this completes my efforts with the P0121. I hope the resistance and voltage (courtesy of TDIClub) information above is helpful to others as you diagnose your own P0121 error. 

Thanks, as always, for following along-