View Full Version : 1994 STS alternator question

07-24-10, 01:10 AM
I just purchased a 1994 STS.
Having a problem with the charging system which i thought was the alternator(only showing 11.5v charging). I replaced the alternator and had it tested before i brought it home and tested fine.
Replaced the old one and am still only getting 11.5-11.7v.

While checking the wire diagram in Chilton i noticed that they show 2 wires coming from the alternator as well as the main to the battery. the main is red, the other two on one connector is red and gray. Chilton shows red to the information display and the gray to the PCM.

Seems mine only has 1 (the red wire).

Should there be a gray wire there also?

If not any ideas on the possible problem with the lack of charging?

Battery good, all connections cleaned and checked, the pcm shows as a remanufactured.

If i AM missing the gray wire, anywhere i can find the pin out of the PCM unit to run a new wire tot he alternator?

Otherwise the car is in GREAT shape 100k no rust or scratches, interior almost perfect (just a couple of floor stains to get out). Just got to get the charging figured out.

07-24-10, 01:54 PM
Slight mistake in my first post... it was they HAYES manual that showed 2 wires.. i just picked up the Chilton one and it only shows 1 wire (the red one).

It was suggested that i run a jumper wire from the battery to this small red wire to "excite" the alternator to throw full voltage. I was told this would tell me if maybe the wire or the pcm was bad...

07-28-10, 07:12 PM
Another update...

Went ahead and put in a new PCM unit.. no luck... still showing 11.5-11.7v from the alternator...

Only thing left is the damn red wire...

ANYWHERE i can find the pcm wire out diagram?? Tracking this wire is going to be a pain in the a$$.

ANYONE??? wire diagram??

09-11-10, 04:36 PM
My voltage is low on my 96 SLS too. Mine is still in the 12 volt range. I just replaced battery and alternator with an AC Delco re-manufactured unit. My voltage actually got a little worse. Next I am going to run another cable from the alternator to the battery so I will have 2 on the same post. I have been reading about a few Caddy's with similar issues doing this and it fixed it because they found corrosion under all the insulation even though the connections were clean. I will let you know if it works and also what wires my alternator has on it.

09-11-10, 05:05 PM
WELL.. after replacing the alternator, then the PCM, and even running a new wire from the PCM to the alternator... i found out the whole problem was actually the connection on the alternator to the PCM.

The repair WOULD have been about $5.00 for the part (might want to check that out on yours helipirate).. but .. about $300 later... (and 3 different PCMs, the other 2 kept throwing me faults on other components) shes at least running.

Now just have to get the ride control sensor replaced... the A/C charged, and new mufflers... Oh yea.. and get the dang CD out of the stereo (it seems to be stuck in there)

09-11-10, 08:02 PM
So it was the plug that you put into the alternator or the part you put the plug in on the alternator?

Thanks for the update, these electrical bugs are so hard to track down.

09-12-10, 06:15 PM
So it was the plug that you put into the alternator or the part you put the plug in on the alternator?

My STS has one wire from the alternator to the battery... (the thick red one)...

Then there is a lockable single small red wire that goes from the PCM to the alternator..(best i can figure is that this sends a signal to the alternator as to how much of a charge that needs to be sent).

The one i replaced is the small red wire connector. I cut off the connector end.. spliced and shrink wrapped (heat wrapped) the splice. Plugged it back in and it started charging correctly.
If i remember right.. it was like $4.95 at my local Advanced Auto store.

09-13-10, 01:27 PM
I got a connector on order, it should be here in a few days. Cadillac wanted $72 for it! I found one online for $10 since advanced auto could not order it for some reason.

09-14-10, 11:15 AM
my 96 sts had same issue. broken wire at plug. i got a used plug at boneyard. seems 96-97 sevilles/devilles had similar plugs. 94-95 cars seem to have single wire plugs. alt tested fine.

09-16-10, 06:10 PM
No luck for me. Changed my connector and still have the same problem :hmm:

09-16-10, 06:11 PM
Also mine was a two wire connector unlike yours.

09-19-10, 05:38 AM
your voltage regulator could be bad inside the alternator