Alternator, Battery, Wiring?

[Hearts88]

Hi, I've got a 1987 Cutlass with the 3.8L engine.
recently having problems with what I thought was the Alternator. Car was draining the battery while driving.

Had the Alt tested and it was GOOD!
So I had the Battery load tested and it came back good.

Here is what I personally have found.

Tester on the batter with the car running. 11.5 volts.
Tester on the Battery Ground and the positive on the Alt. 11.5volts
Tester with the Ground on the ALT and Positive on the ALT 15volts
Tester with the Ground on the Alt and Positive on the battery 15volts

I did this with the headlights running and the car at idle speed, I believe about 650 or 750RPM's.

Anyone tell me what is going on. Why do I keep draining the battery.
Is my Ground from the battery to the Engine bad? Should I replace the ground battery cable?

Or the positive cable? Or both?

Anyone that can help...please do... I have no freedom as I can only get to work and to home, and have to charge the battery everyother day or I am not going anywhere.

Thanks
Hearts88

[GTP Dad]

The problem is that there is a wiring issue. Probably the main battery cables have gone bad and need replaced. Also check the fusible links at the starter as one may have blown. With the engine running you should see the same voltage at the battery as you see at the alternator. 11.5 volts is way too low and the reason you are draining the battery is because the voltage from the alternator is not maintaining the charge and you are depleating it rapidly. You also need to make sure that your grounds are good. A loose ground wire at the block can cause a failure to charge as well.

One thing you may want to do is to charge the battery with a charger after you find the wiring problem.

[69-cutlass-S]

Did you install a new stereo or something else lately? It sounds like you have a problem with your wiring somewhere in the car. If you have a good positive battery cable and a good negative battery cable, then you have a wire somewhere else in the car that is grounding to the chassis and draining your battery. I recommend you check for amperage draw at the battery. While you hold the tester leads on the battery posts and read the amperage, have someone pull fuses one at a time until the amperage draw stops. That will isolate the circuit with the wiring problem.

[Hearts88]

GTP dad,
Fusable link at the starter?
What do you mean exactly. What should I be looking for at the starter?

69-Cutlass-s, nothing has ever been added to the car. Everything in it is original. The car has been family owned since new(wife's family). As far as I can remember in the last 3 years we have owned the car it has always been kinda a low charging car. Not as bad as it has been these last few weeks. We have taken this car on long road trips and it has been our daily driver.

This Amperage test, when they pull the right fuse the Amps should go down?
and when that happens it means that something that is hooked up to that circuit is causing the problem?

Thanks guys, I will start by replacing the battery cables... oh one more question... should I replace the battery cables with 4 gauge or 1 gauge or does it matter?

Thanks.
Hearts88

[DANGORDON666]

you may not have realized it but you found the prob. with the meter cuz when both leads are on the alt or when positive is on batt. you get charging voltage so neg cable has bad conn. to double check this try grounding at other places on motor and on body,if you get 15v from grounding on motor but not on body or frame it is probably the braided motor to frame ground.
also try detaching the neg batt. cable at both ends and cleaning conn. points with wire brush and recheck with meter. also if you are putting 15v to the battery you may have a voltage regulator problem and should have alt rechecked,voltage to battery should be 13.5 give or take .5, 15 volts on a long trip esp. a daytime trip will eventually mess up the battery