Ok I feel very dumb the alternator on my Baja bug 2.4 ecotech swapped motor has been inconsistently charging. Pulled the whole thing apart and had the alternator tested. Tests out fine. I was told GM alternators are single wire but there is a plug on the top of the alternator going deep into a mess of a wiring harness. Test that wire for continuity and it breaks as it flexes and the wire is literally just jammed into the plug. Run a new wire and properly set it this time and sure enough it charges to 14.3v as soon as I bring on the revs's.
What the heck does that wire do. Looking at my harness it seems to go to the 12v key on portion of the harness but its hard to tell. I have been running true one wire alternators on the carb'd stuff for so long I don't think I have seen this before.
Alternator excitor for the regulator? 12V to only charge on a low voltage battery?
Pretty sure that wire is used by the internal regulator to sense the voltage that it's trying to regulate. You can just connect the sense wire to the output and it'll produce 14.3V at the output. There's usually some voltage drop through the harness, though, so voltage at important places like headlights might be a lot less. If you run the sense wire back into the harness the regulator will see a lower voltage and produce more at the output so that you get the right voltage where it matters.
If you have 3 wires the third one is for the alternator warning lamp.
http://www.madelectrical.com/electricaltech/remotevoltagesensing2.shtml
I'm 90% sure it's for a warning light if you want to run one.
Its been too long since i had looked into it, but i recall the gm "1 wire" alternators still need another wire to work right
If it is the one im thinking of, its the excitor wire. It should go throug a bulb as a charge indicator, and to protect the windings. The other spade terminal goes to the charge post to sense system voltage. Then the charge wire to the battery.
I don't know how or if this applies to a swapped VW but . . .
As I vaguely recall stock VWs "need" a wire going to the bulb on the instrument (speedo, etc) to run. I believe it came from the generator. Perhaps that isthe wire you are dealing with. My VW info source is theSamba when I need it.
