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CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

Not being a real whiz with electrical stuff, I thought I'd best ask the Board before I start taking things apart...

Going into town this morning I happened to glance down at the volt meter and I thought I saw it "blip", then settle below the 12 volt mark. A quick flick of the blinkers showed that the gauge was working (dipped as the blinkers went on and off), so I got off at the next exit and headed home "just in case". Well it is a good thing I did, because after putting the car in the garage, and immediately trying to start it again, nothing. Not even a click from the starter solenoid. Belt is tight, connections - including the ground strap - are clean and tight. The only other alternator-related problem I've had is that when starting the car, the idiot light stays on until I tap the throttle and bring the RPM up for a second, then the light will go out and stay out even after the engine settles back to idle.

Trusty multimeter shows 11.9volts at the battery. After starting the car with jumper cables and disconnecting them I get 11.6. No difference if I rev the engine or not.

I didn't start poking around the alternator contacts, not knowing which terminal should show what or when. Haynes just says that the battery should be in the 13.5-14.5 range when under load, but doesn't say anything else about what to test or how in order to isolate what the problem might be.

Any advice before I pull the alternator and take it to Auto Zone for testing? Is there an easy way to tell whether it is (likely) the regulator or the alternator itself? Pic below is what the back side of the unit looks like. Two terminals, "B" is the large one with fat red wire, "D" is below and left of it with a blue and black striped wire (is this the "exciter" wire that was written so much about not too long ago?)

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'79 Eurospec 931

Paul · Posted: Sun Mar 13, 2005 9:15 am Post subject:

The only way to check the regulator is to swap it out.

I'd just yank the alternator and get it tested, on a 931, they are pretty easy to remove.

Have them test it. then buy a regulator while you are there, pop it in and have them test it again.

Paul · Posted: Sun Mar 13, 2005 9:18 am Post subject:

Yes the blue wire is the "exciter".

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

That ground cable looks a little beat up.I would try a temporary ground first before I pulled it.
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1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Ozzie · Posted: Sun Mar 13, 2005 10:59 am Post subject:

The most common problems with alternators is the brushes.
If you unscrew the black box from the back of the alternator you should find the brush gear is worn out..
If they are OK then the fault could be either the regulator or the alternator itself.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Llamaguy · Joined: 02 Jul 2003 Posts: 711 Location: Indiana

measure the voltage at the battery when you turn on the lights, once before tapping the throttle and once after, and see if the voltage is goes down; this will tell you whether the thing is charging.

Also, Autozone wouldn't test my alternator, Advanced autoparts would, and the guy even use to have a 944 which was kinda neat.
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1987 924S Guards Red
1997 Suzuki Tl1000 Supersport