[DML] Alternator problems

["Dave Swingle" <swingle@xxxxxxxxxxx>]

Rich and I were working on an alternator issue today that I've never 
run into. I know how to look for the usual stuff, but this one has me 
stumped.

Start car - alternator light stays on, charging system at 12.1 volts 
(DVM, not the dash gauge. Dash gauge looks to be about 9 volts). 

Rev Engine - charging system jumps to 13.9 volts, light stays on. 

Let it idle back down, stays at 13.9, light stays on. (Dash just 
above the 13). 

Things we tried - remove light bulb - acts exactly the same (but with 
no light - duh). Checked wire (brown w/yellow trace) from alternator 
to idiot light with both ends disconnected - no shorts to ground, 
overall resistance of the wire less than an ohm. Cleaned up bulkhead-
to-frame ground, bypassed engine-to-frame ground, check all 
connections at instrument cluster. Checked connections at alternator 
(all those stupid brown wires). Tried another battery. Keep in mind 
that the car starts and runs fine, which rules out most of the 
grounding issues since the starter ground and alternator ground are 
essentially the same path. 

I'm suspecting that the regulator in the alternator is bad, but we 
tried three different used OEM Motorola alternators (all of 
admittedly suspect quality). Unfortunately I'm not sure the other two 
worked the same - we didn't try reving the engine with those. In all 
the cases the idiot light was on brightly. 

Next step is to replace the alternator with a new one, but did I miss 
anything? 

Dave S





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