Chasing the Hapy Electrical Gremlins (part 5)

Continuing the saga of re-doing the TDI-related wiring in the bus. Recall, this all started because I was not getting consistent signals at the computer from the accelerator pedal, 20 feet (7m) away. I got carried away with some wire cutting and suddenly, rather than just replacing the front-to-back wiring, I was replacing the fuse box. Today's post is about the wiring surgery.

Expose the Harness

I started simply: set the main harness on the kitchen table and then spend hours trying to figure it out. Many of the wires were still hidden within stretches of cloth tape, so that was the first task: cut that tape off. This is simple, but messy because that tape remains tacky. This black tacky ick gets all over your fingers, and sticks to things, like your kitchen table. My wife loves me. I found that Goof Off was very helpful getting the sticky off of the wires (and the kitchen table). Once all of the wiring is separated from the wraps, and wiped down, we can start thinking through the various wires.

Wiring

My first order was to consider how much length I needed between the different pieces. For example, the distance from the bottom of the fuse box to the dashpod is less than a foot. In between them, I have the pass-thru hole below deck. I figured that the cleanest look from up-top would be for only the connectors to be above. So, that moved the T10 connections below, but I wanted them close. So, I shortened the wires from the main harness to the T10 connectors so they were all close together. Into this mix, I
added what I labeled a "T12". I purchased a 12-pin male and female connector to go between the front-to-back cable and the main harness. This is so that I can disconnect it like the T10's. Once the T10's were at length, I started integrating the T12. Not all of these connections go directly into the main harness though. Reference the post listing the T12 here. Circuits 1-6, 8, 9 and 11 tie into the main harness. That left 7 and 10 for the next step: the fuse box.

With the final extra wiring removed, the T10's arranged and most of the T12 integrated, it was time to consider the fuse box. I had already defined where in the bus it would be, but it also needed to be located in the right place within the harness, so the wires were not stressed, nor flopping all around. I used the dash pod plugs as a reference point, and considered the plan above as I decided. Since the middle of the harness will be below-deck, it was okay for the wires to be a little long. Once the location was determined, I started thinking about the relays. The relay box has 6 relay slots, but 5 are designed for standard Bosch relays (30-85-86-87 pins, with a middle pin for 87a). That's great for my start and run relays, but not so great for the glow plug (180) or main power (109) relays. Those have particular pin patterns. So, getting them to integrate with the pre-formed relay slots would take some customization.

 

Integrating the Donor Relays

I had designated on my wiring diagram that relay slots 1 and 2 would be the glow plug and power relays respectively. In the original relay plastic, they used to slot into #10 and #12 respectively. Each of these original plastic retainers have a little cut out to allow the fit of a specific relay holder. Fortunately, #11 is exactly like #10 (while #12 is different). I realized I could cut #11 and #12 out of the original retainer, clean them up and super-glue those retainer into slots 1 and 2. With some careful cutting with a hacksaw, I removed the 2 holders, and managed to fit them into the fuse / relay box. In order to interact with the wiring for the fuses, I needed to clearance the top, front edge. Also, because of the super-large size of the 180 and 109 relays, as well as the size of the relay retainers, they are super-glued in along the bottom edge, leaving about 1/4" of overlap for the super-glue to hold. Still, super-glue is amazing stuff, and with just that little edge, these original retainers are absolutely held fast, even when I put a little wiggle-pressure on the wires.

Fuse by Fuse

With the original relay retainers in place for the 2 big relays, I was ready to get after the fuses. Now, recall that I had this bus running with about 7 of the original fuses still plugged in. I discovered, however, that I really only need 4 of them: 29, 32, 34 and 43. I still had fuses 11, 12 and 15 plugged in and wired up, though. I have ported all of them over. Former fuses 11 and 15 share a fuse in the new box (fuse #1) because they appear to not really be necessary, but the wiring was there, so they are wired up now. Fuse 12 (now fuse 2) is to supply power to the OBD-II port in the wiring compartment. I expect this to be consumed almost never.

 

The other 4 had been clearly marked during my label-label-cut process. I had left myself plenty of wire so I did not have to extend any of them, which was very fortunate. For all of the fuses, the "consume" side is the front or furthest-from-the-relay side. As I wired in, I set the wires down so they would exit the fuse / relay box towards the front. Next, I did the supply side of the fuses, wiring fuses 1-3 together and then over towards the "RUN" relay and fuses 4-6 together and then towards relay 109. In the wiring diagram, fuse 29 gets it's switched power from the ignition, not through relay 109 so this is a correct reflection, though a little weird. I think it is through this circuit that the ECU is notified that the key is in "RUN" so it should trigger relay 109.

Relays

So, the fuses are done, the relay retainers for 109 and 180 are super-glued in. Next, we get the other relays wired in. I actually did 4, but I am only going to write about the "RUN" and the "START" relays. The other 2 I'll get to later. RUN and START are basic Bosch-style relays. A signal arrives from the ignition switch into pin 85 or 86, that signal difference is compared against a ground at the other 85 or 86 pin. Once triggered, pin 30 is connected to pin 87. So, for our purpose, the pin 30 for both of these is connected to always-hot, the 86 pin is grounded, the 85 pin wires into the T12 (7 for start, 10 for run). Pin 87 is where things get interesting. Pin 87 from the START relay connects to T6 to send a start signal to the starter. Pin 87 from the RUN relay connects to fuses 1-3.

 

Similar to the relay set up I had before, I wired in a one-way diode between the START trigger and the RUN trigger. Recall, this is because some ignition switches will not send a 12V signal down the RUN circuit while sending one down the START. When this happens without that diode, the second you try to start the engine, the computer thinks you turned the key to off, so it won't start. This diode allows 12V across from the START side to the RUN side, but not the other way. With a multi-meter, you can check this: negative on one and then the other, you can read connectivity, but only one way. Very cool. Last, the reverse light signal will be integrated into the switched circuit, but that is the only bus-related cross-wire (with an integrated fuse. of course). I did that because switched power was needed, and the consuming wire for it going to the switch on the transaxle was less than a meter away.

 

Last, I did the wiring related to relay 109, leaving the always hot circuit 30 to be determined once I got back out to the bus. Without that all the extra relay stuff, the hot wire had been cut out. I can now see that the actual demand on the 109 will be minimal (like 30A) in my implementation, so I will be replacing the old 2ga supply wire with a smaller one.

 

Once I was satisfied with the kitchen table wiring job, I took the whole contraption out to the bus for a test fit. Everything looked workable, so I brought it all back inside to wire-wrap. I used that plastic tube style available at Harbor Freight for all of the wiring clumps that run from a plug to the main harness, and from the fuse / relay box to the main. This left a few wires that still have label tags on them for things like the alternator signal and the coolant level. Both of those (alt and coolant level) are related to idiot lights I wired into the 6-wire cable when I did the oil pressure stuff (see Oil Pressure and Temperature - Part 4) so I will deal with those once I get out to the bus. All of these little wires have a partner in the engine compartment, so I will solve for them as part of the next phase: install.

That's all for today. This literally took me days. After many years of working at a place that shut down between Christmas and NewYears, I have grown very accustomed to having that week. In past years I have redone the seats in the MG or rebuilt a front end. This year, I spent most of that week doing the wiring, fuse / relay box stuff I just described. Yeah, this is a serious time killer. But, if Hapy starts on the first try, doesn't drop into that 1200RPM mode ever again and the wiring is no longer an eyesore, then it was all worth it. Thanks, as always, for following along. Please keep wearing your mask. These CoViD numbers are still very scary--