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Tue May 06, 2025 3:24 pm

1972 Bus. Motor was out for rebuild. I re-installed it today. No issues except this wiring question.

I replaced the alternator harness as the old one was crusty. The new one did not include the black wire that formerly went to the "test network" and that's fine by me. I tossed the old harness but I'm pretty sure there was no black wire on that one either (more on this later).

Before I pulled the motor I was pretty diligent about labeling things. But now I'm not so sure.

The paired wires at the one connector (one is green and yellow, the other appears a dull greenish-blue) I'd labeled "to green wire". Now I'm wondering, what the heck? Looking at my wiring diagram (Bentley) and around my engine room, I don't see a green wire that would make a logical connection. I'm also thinking the blue wire from the alternator harness should be connected to those paired wires (and not the black wire, which I could have sworn was the way it was hooked up before), and that maybe the black wire had to do with the old test network. Except the black wire here appears to run into the harness up front. And though my Bentley shows a the blue wire splitting at the connector--one goes up front, and one to the blower relay--the wire that I have going to the relay is green and yellow, versus the blue shown in the diagram.

(Side note: The blower has never worked since I owned the Bus, but I didn't mind it. As a curiosity, I bench-tested the motor while the engine was out and it works just fine. So maybe it was wired wrong from the P.O.?)

So, either I really mislabeled something or it was already mis-wired previously. This Bus is pretty original, and I can't recall any examples of P.O. wiring hacks. Regardless, I'd appreciate being pointed in the right direction here, thanks.

Tue May 06, 2025 4:19 pm

The one you are calling green looks blue from here to me, the blue/yellow is an odd combo for that circuit but VW has subbed wire colors in the past if they were low on the correct stuff.

That blue wire from your new harness connects to the blue (or green?) wires that go into the connector with the blue tape on it.

Wed May 07, 2025 5:14 am

busdaddy wrote: The one you are calling green looks blue from here to me, the blue/yellow is an odd combo for that circuit but VW has subbed wire colors in the past if they were low on the correct stuff.

That blue wire from your new harness connects to the blue (or green?) wires that go into the connector with the blue tape on it.

Okay, that makes sense, thanks. But what to do with that black wire? Going by standard VW wiring conventions black would mean switched hot, but I have no idea what this would power. Wishing I'd done a better job photographing/labeling before I took everything apart.

Wed May 07, 2025 7:22 am

BruceJ wrote: ...... Going by standard VW wiring conventions black would mean switched hot,..........
Correct, but in this rare exception it's test network terminal #14, tape it up.

Wed May 07, 2025 8:17 am

busdaddy wrote: BruceJ wrote: ...... Going by standard VW wiring conventions black would mean switched hot,..........
Correct, but in this rare exception it's test network terminal #14, tape it up.

Ah, the orange spot #14 on the diagram, with the connector for the black wire that would've originally led up to the alternator harness. Though I do wonder where the other end of this black wire goes after it disappears into the harness forward, I'll go ahead and tape it up.

Thanks for clarifying things, BD. 8)

Wed May 07, 2025 8:31 am

Is the GEN dash light behaving properly? If so, it's wired correctly. The blue alternator wire goes to the GEN dash indicator. Normally, the mating body harness wire is a single wire.

Wed May 07, 2025 9:00 am

telford dorr wrote: Is the GEN dash light behaving properly? If so, it's wired correctly. The blue alternator wire goes to the GEN dash indicator. Normally, the mating body harness wire is a single wire.

Yes, it was before I pulled the engine, and the alternator was charging just fine. And I thought the same, one blue wire to one blue wire, although my Bentley clearly shows (now that I've studied it) a Y-connector with second wire going up to the blower relay.

I'm thinking that I'll wire it up as BD suggests. The first test will be if I get the GEN light when I turn the key ON (not start). If no light (along with the oil light and, if I recall, brake warning) then I have some further sleuthing to do. Sound about right?

Wed May 07, 2025 9:43 am

Are you sure that “black” wire is black. Peel back the sheath near the grommet and expose some clean wire insulation to confirm it’s not just oily scum hiding the actual color.

Thu May 08, 2025 11:03 am

Okay, I rewired a few things, fired it up today and all is well! GEN light does what it's 'sposed to, and charging system seems fine.

While I was reaching in to re-do the wiring on this, suddenly I realized that a quick (and now obvious) test was staring at me right in my face--the network terminal, which I'd pretty much ignored until today. So I clipped one end of my VOM to the black wire by the firewall, stuck the other probe into where a black wire goes into the terminal, and whaddya know, continuity! I guess it threw me off that while the black wire -looks- like it goes up front, it actually doubles back and goes up to the terminal #14 (as has been suggested).

So, all good I think. . . .thanks for setting me straight!