Had my abs and charge warning lights come on at a race recently. Car still ran fine, but I need to get this fixed. I looked at datalogs from the race and voltage was bouncing around (between 12 and 14) more than normal. Firgured it was alternator and replaced it. Still have same problem so figure it is really a wiring prob, but not sure.

Symptoms...

-abs and battery light on
-when car starts up idle voltage is 11.5 (low)
-blip the throttle a bit and voltage goes up to 14.0 and holds steady
-but warning lights still on

When you put in a new alternator do you have do do anything special to set it to charge at idle? I should mention car normally idles at 1300rpm (not a street car).

Any ideas welcome. I'll be looking at the wiring for shorts and make sure the battery is ok.

TIA,

Andy

 

Get a multimeter and measure the voltage at the following points when the engine is running:

Connect one lead to the Alternator post (+) and the other lead to the battery post (+): should measure a very low voltage, less than 0.5V on the meter.
Alternator case (-) to battery post (-): should also be a very low difference, less than 0.5V on the meter.
Battery post (-) to chassis (-), same thing, want low voltages.
Battery post (-) to engine (-), looking for low numbers on both of these.

A high voltage number usually indicates a broken wire or poor connection.



If you have trouble finding anything, get a helper and have them tap, wiggle or gently tug on these wires while you measure them.

 

Everytime I have seen an FD alternator fail the warning ligts on the dash come on. I think once the car drops below 12volts the lights are triggered on the dash. It has been a long time since I have really looked into it, however the battery and abs light almost always mean it is a alternator issue.

 

Thanks for the suggestions, I'll double check those when I get back to the car. As much as I've been able to check the main power wiring all looks good at the alternator and battery.

The weird part is how when you first start up the voltage is low (not charging). Rev it a bit and the alternator starts charging steady. It stays charging even back at idle. Weird. Only thing I could think of was poor connection that needs a little extra current to bridge the gap, then stays connected. In any case, the warning lights stay on which is annoying. My guess is there is still an issue with the W/B wire off the alternator since it goes into the oil level light, abs, exhaust overheat, and charge lights. All those are on.

-Andy

 

Are you 100% sure that the altenator you installed is a good one ? Have autozone check it

Later

 

Did some of the service manual checks at the 3 alternator terminals (B,L,S).

With ignition ON I get...

B = battery V
S = battery V
L = 0.0 (resistance check says it is same as ground)

Start car and idle...

B = battery V (low)
S = battery V (low)
L = 0.0 ** this should show some voltage

Blip the throttle to get the alternator started and let return to idle...

B = charging voltage
S = charging voltage
L = 0.0 **this should show some voltage

Manual says if you fail these checks to replace the alternator or there is wiring issue. I can't find anything wrong with the L terminal wire (White with black stripe). Can someone check theirs and tell me if that is ground with the car off? If it isn't ground, I've obviously shorted that wire somewhere.

Thanks,

Andy

 

Well, still frustrated at this one. The one W/B wire from the alternator goes back to the rear of the left front wheel well, where it splits. One leg goes eventually to ABS in back of the car, the other to the instrument panel wiring. I split it and the ABS side is not grounded. But the instrument panel side is grounded somewhere. I'm still assuming that this is wrong and there is a short somewhere in the instrument panel wiring. However, trying to trace farther is a real bitch since those connectors are real hard to get to. This sucks.

Any ideas appreciated.

-Andy

 

OK, fixed my own problem. I kind of doubt others will have the same issue. After tracing the one alternator wire back to the instrument panel harness and not finding any issues, I was getting pretty pissed. However, the logical part of me was saying that it was doubtful anything would spontaneously go wrong deep in the factory harness that I never screw with on a car that doesn't actually get much usage (albeit very hard usage when it does).

So the instrument panel harness goes across the front of the car under the dash, but also goes into the center console by the shifter. Hey, I've been in there before maybe I messed something up. I'd already looked there and not found anything, but went looking again. Found I had pinched the factory harness against one of the shifter insulator studs (rubber piece under the shifter). Peeling apart the harness showed two wires had barely rubbed through the insulation. One of them ohm'd out to be the same wire as the alternator wire. Got that separated away from the screw and all was good.

I farking hate wiring crap sometimes. Thanks for the suggestions.

-Andy