Question about 1995 Oldsmobile 88

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Alternator not charging

When car is running, the alternator big connection has only 12 v. or less. Alternator checked out good at autoparts store. I think Someone has miswired the lead going to the regulator when he replaced all the lights in front of the car. There is only one red wire going to the regulator, the plug has 4 prongs, 1 big and 3 small. I measured, but there is no voltage on the regulator wire whether the car is running or not. I think something has to energize the alternator through the reguilator for it to charge. Is that true? So there has to be some voltage on the regulator prong? But I don't know where is it wired to.
Please help.

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  • jcorjoe Jan 16, 2009

    I had both the big hot wire (A heavy black wire) and the regulator plug (which only has one small red wire) connected to the alternator. With the car running on idle, the voltage on the battery + and the big hot wire on the alternator are the same, barely 12 Volts. That's not enough to charge the battery. Is the alternator itself or the built-in regulator inside the alternator bad? The wiring schematics shows the regulator red wire is connected to the Powertrain Control Module. Where is that module in the car?

  • Jon B
    Jon B May 11, 2010

    "big hot wire and battery are directly connected" sorry left some of that out, been a long day..

  • Jon B
    Jon B May 11, 2010

    the power train control module is what the coil packs are bolted to. and the big hot wire are directly connected, so you will get the same reading. And in most cases when the module goes out it burns the the side out for the fuel injection. Yet if the regulator internally is failing, it will show a swing of 11-13.5 volts, and the car you have doesnt care about the volts, its main intrest is the amps, those alternators are generally 110 or more amps.And the olds uses alot of them.

  • Jon B
    Jon B May 11, 2010

    The large red wire reading is a reading from the battery. And those models die if you remove the terminal weather it is good or not. Someone will suggest that. Try testing the alternator somewhere else, It may work once in a while, as they sometimes do when you remove it from the car for a test. Be careful poking a ohms meter on the back, the regulator is sensative and the manual warns of regulator failure if you attempt it.


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Joe, there is no longer a regulator on this car as we would know it to be. The ecm is now also resposible for telling the alt when to turn on and off. This was done in order for the alt to be turned on and off in conjunction with the other loads and engine speed in order to be more efficiant in the long run. So from what I read here, you either have a bad wire somewhere or your ecm is toast. Replacing lights-unless for some reason the wires were cut(doubtfull) would have no effect on the alt.

Posted on Aug 25, 2009

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