TDI install retrospective: Primary Electrical

Continuing the process of back-documenting what I did to put a TDI engine into an old (1972) air-cooled VW bus. Today I cover the Primary Electrical. It probably makes sense to start with what do I define as "primary"? To me, this is the battery / alternator / starter relationship. To be fair, the engine won't start if only these pieces have been solved, but I needed to cut this up, and this was how I thought of it when I did the original work. Before I begin, Hapy Christmas.

Battery

Of all of the electrical parts, this was the easiest part, as you probably assumed. Simply put, get a battery rated for your engine. Consider that the battery tray is definitely long and wide enough for a large battery, but there isn't much headroom. Some of the batteries are fairly tall, and you will need to put the battery-top fuse box on top of it. The usual battery is a group 94R, and though I have read of folks using group 44, I would encourage you to use the biggest battery you can. The 94R fits. Using the donor positive battery cable (you got that, right?), wire up the battery-top fuse box and run the main line to the alternator and starter. I had to extend the run to the starter, but I was able to reuse the run to the alternator without cutting it. I re-used the bus-original ground cable, grounding against the block behind the oil cooler as well as against the body. Once you have confirmed your runs, I strongly suggest you disconnect one or both from the battery.

Alternator and Belt
Use the alternator that's already on the donor engine. This seems obvious, but you may be tempted to upgrade the alternator. This could fall into the "while the hood's open" trap of changing so many things you can't figure out why it doesn't work. So, pick your initial upgrades carefully. The larger alternator does fit right in, and with the access hatch, or even with out it, getting to the alternator on the TDI is way easier than getting to it on the old air-cooled engine.

Taken from the original post about the belt (All Work and No Play...) the correct belt to run the alternator when you don't have power steering nor air conditioning is GoodYear (part number 4060295) - 29.5" effective length. It pops right on, held snug with a tensioner that can be eased with a 5/8" crescent wrench on the exposed nut. Thread on the cable from the battery and plug in the plug from the engine loom, if it had become detached.

Starter

starter adapter

The original bus starter will not start this engine. There's no point in trying. Sell it instead. If you didn't get the donor starter, these can be expensive. I was very fortunate, and Justin gave me one that was making noise, but still worked. I have since had to replace it (the noise foretold it's weakening, and it eventually broke). Now, the TDI starter will start the engine, but it will not fit into the starter hole in the bell-housing. Remember the starter adapter I mentioned in the preparation post (See TDI install retrospective: Preparation)? They are from Westy Ventures (buy here). When I bought mine, they did not have one that fit the 002. So, I got the one for the automatic which was closest thing they had and trimmed away aluminum with a Dremel until it seated properly. Basically, I would dab some grease on the adapter and test fit. Where the grease had smeared off, it was hitting the bell-housing, so I'd trim a little bit. Wash-rinse-repeat until the adapter sits flush. Then bolt it up and then bolt on the starter.

Primary Wiring
With the alternator on and wired and the starter on, we're ready for the final piece: wiring up the ignition control. This took a considerable amount of time and research and the help of AndyBees. There are so many posts back in 2009-2010 as I wrestled through this, I couldn't possibly post all of the links.

First, we had the clutch pedal lockout. This was jumpered around at relay #3 (185 printed on it) so the starter will engage regardless of the clutch pedal position. Because of the weird nature of the wiring, it seems like other things could also prevent starting, like an open door or something. This is why we jumpered the circuit rather than fake a pedal switch. Oddly enough, I used the lack of this switch to move the bus around the driveway with the starter once. I don't recommend it, but in a pinch....

The computer needed to know when the key was in the "run" position to trigger switched circuits. I ran a wire from the fuse-box at front of the bus from a switched circuit back to the spare tire well where all the wires and the computer for the TDI reside. I had this wire trigger a standard relay to send 12V to the TDI ignition switch. After we suffered the ignition fire (See 4Peaks 2018 - Road Report), I moved the "switched signal" to come directly from the ignition switch circuit rather than piggy-back off of a random switched circuit as I had it before.

Out of respect for all of AndyBees' work and because he asked, I'm not going to post a picture of the ignition switch diagram. I will stress the importance of sending always-on power into both of the #30 female clips in the switch. This just needs to be signal-strength thin wires, sourced from a fused, always-on circuit. I am sure that if you asked (on TDIClub) he would bend over backwards to help you.

Last, we want to notify the computer that the switch was moved to the "start" position. I extended the original trigger wire from around the starter back to the engine bay, along the firewall to the passenger side and then up to spare tire well. This was also wired into a relay similar to the "run" circuit. Because of the manner of the TDI ignition switch, the "run" circuit needs to be energized when the key is in start position as well or the engine won't start. Since the bus is not wired that way, I wired a one-way diode (like this) from the start signal to the run signal to remedy: regardless of bus switch position (run or start), 12V is going into the "run" position of the TDI ignition. Then, from the other side of the TDI ignition, I traced the starter signal wire and extended it to the trigger plug on the starter.

Lots of text there, but basically, I extended the wires from the bus key back to the computer sitting in the spare tire well by using some bus wiring, some new wiring, a couple of relays and the TDI ignition. I have revisited the spaghetti of wires in the spare tire well before, and I intend to do another round to really tighten it up, but the wiring design as described above works, and has supported the TDI-in-bus for almost 10 years with an annual disconnect/reconnect cycle for the wires to relays and donor ignition switch.


Prior related posts:
Preparation
Fuel System
Physical Mounting
Vacuum System
Air, Inter-cooler and Exhaust

Next related posts:
Cooling
Secondary Electrical
ECU, dashpod and Sensors