A Thought on Altenator Exciting

[maxfax]

Have you tried jumping the D terminal to B+ to see what happens??  That would rule out anything with the alt such as a funky regulator or something..   My bet would be, though, the low voltage at the D terminal is your culprit..  I had similar issue with one of my MK1's years ago..

 Never tracked down the real problem though..  The car was junk and I'm kinda lazy so I ran a switched B+ to a light socket with a 194 bulb duct taped to the dash, then from the socket to the D term...

[somolovitch3]

Yep, that is what inspired "thought" in first place. Temporally hooked small jumper lead from D+ to Pos on Batt, instant excite at start and kept up 14.3 voltage at idle when removed. New-ish thought, since starter has a terminal to feed ign while starting (on the diesel starter of all things) run a wire thu diode to D+ from there.

Voltage drop in Alt LED circuit....2 volts for the LED, aprox. 9 volts at the 470 ohm LED resister (keeps the 12v from frying the LEDs), and who know on the big (1 watt) resister. And I have 4.8 volts at the D+ term with key on, engine not running. I hate math.

[TDDrew]

Sweet! Did you try a regular bulb yet? I was thinking about rewiring the light bulb so it would not interfere with the current flow to the alt excitation. 

[somolovitch3]

Not sure how to install one, the LED plugs into the (wonderfull) Circuit Board using it's leads into clips molded into the Circuit Board.
Hard to change that to a lamp setup. And I wonder if there is some reason that VW used a LED any-way, as a diode to seperate circuits?

[maxfax]

I suspected it was just for longevity..  I bulb usually doesn;t last as long as an LED, and on that paticular setup, if the bulb blows it stops charging with no indication to the driver..   

[TDDrew]

Not sure how to install one, the LED plugs into the (wonderfull) Circuit Board using it's leads into clips molded into the Circuit Board.
Hard to change that to a lamp setup. And I wonder if there is some reason that VW used a LED any-way, as a diode to seperate circuits?

Ohhhh, what car are you working on? I was talking about my A1. It would be nice to be able to check the volt drop on a good working one.

[somolovitch3]

This would be the DumBuny, 1984 GTI Sport (ish).