Alternator dont Charge - red warning lights are on

[SJ]

Symptom: alternator is not charging

Things tested:

1. Started engine and tested voltage at the alternator.
Big post -> 12.0 volts
small post - blue wire -> 1.9 volts
Swapped out the Voltage Regulator with a known good one -- same symptoms.


New test just completed:

Disconnected blue wire from alternator to see if wire was ok and was not
'High Resistance' - open or bad contacts.
Started engine
Voltage on disconnected wire is battery voltage - 12 volts.
Put a load on the wire(small light bulb), voltage on wire is  3 volts,  and
bulb glows. Wire is ok.


Diagnosis:
I suspect an internal short or low resistance between the alternator blue
wire post and ground.
An open circuit would read 12 volts at the post with blue wire connected.
A short would read 0 volts at the post with blue wire connected.
A reading of  1.9 volts is telling me that a low resistance exists between
the blue wire post and ground.

Questions:
1. The normal voltage reading on the alternator blue wire post should be 12
volts, right? The same voltage that exists in and around the ignition switch
feed?
2. The blue wire feeds the voltage regulator input?
Does it connect to anything else? I think it feeds the rotor winding at
engine start . . to get the alternator to start charging.
How does it disconnect from that after engine start?

Time to look at the schematic and wiring diagram.

SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q



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