Possible bad alternator

[ty86300zxt]

Recently replaced my 86 Turbo Alternator with an AC Delco remanufactured Alternator. It has been running fine for a ew months but this past weekend came out to a totally flat / dead battery. had driven it probably 24 hours before hand and it had started and drove fine. Next day when i went to drive it was totally dead. Took the battery and put it on a charger and now when i've put it back in the car and connected i'm getting the Charge warning lamp on when the CAR is off. Car starts and drives fine and when the car is running the Charge Warning lamp is off as it should be and seems to be charging the battery fine. but as soon as the car is turned off the charge warning light comes on and stays on - which of course will drain the battery pretty quickly.
Am i right to assume that there is an internal short in the alternator that is most likely providing power to the charge light when the car is off?

[Z_Karma]

You'll probably have to do something called a parasitic drain test to determine what is causing the drain. Usually this involves removing fuses until the current draw drops, but i would see if it drops when you unplug the alternator plug. I've had parasitic drains from the anti theft system, but never had a alternator be the cause.

[ty86300zxt]

I’ve had theft warning fuse pulled for a few years now. But since this charge light issue started last week I went and pulled all the fuses and relays and this bulb remains powered on when the car is off. Since the bulb is directly wired to the L terminal of the alternator I can only assume bad alternator that has an internal short would be the most likely way it could still have the bulb lit up. I just can’t find any info on the internal wiring of the alternator to know what the L terminal is connected to within the alternator normally. I’d assume the diodes or the regulator. And something has failed causing it to ground and turn on the bulb. With ignition switched to acc. Charge bulb should light up. In my car now it does the opposite. Charge bulb goes off when car is switched to acc

[mwolvinm]

That charge warning light should be on when the car is off. If the engine isn’t running, it’s not going to charge. I suggest taking the car to the parts store and doing a full electrical test. They can test the battery and alternator for free. I wouldn’t be surprised if the battery has a bad cell. Other possible causes is a loose/dirty ground or loose connection at the battery.

[ty86300zxt]

My car is doing opposite of what it should. With the key in the ignition and it turned to acc all of the lights should come on including the charge bulb. With the car off and key removed from ignition most lights should be off including the charge bulb. My charge bulb is on when the key is not in the ignition. If I put the key in the ignition and turn it to acc the charge bulb goes off. That is incorrect and I can only assume it’s a short from the alternator. Car otherwise starts and runs fine. Charge bulb is off while car is being driven and alternator is charging the battery. Th issue is really the charge bulb remaining powered on when the car is off and draining the battery. L terminal of alt is directly connected to that bulb but should keep the bulb off when car is off until ignition is switched on. I would guess Alt has gone bad and is shorting the L terminal somehow. Even with relays and fuses pulled the charge bulb remains on with car off.

[mwolvinm]

Yeah…. You have a short somewhere

[ty86300zxt]

FSM EL-25 says that with the ignition switch "on" and the charge light "off" that i need to disconnect the S,L Connector on the alt and ground the L lead wire. WHen i do that, if the light comes on for a Mitsubishi that i have a damaged IC-RG or bad A.C.G. obviously i will try that.. but from best i can tell.. that is what is happening when my car is completely off - that the L lead is being grounded by an internal short in the alt.. turning that light on despite the ignition being off.
They have an extra note in the FSM on that page to say "with alternator side L Terminal Grounded, internal short occurs when Positive Diode is short - circuited.
so i'm thinking that's my answer right there. I originally suspected that maybe i had a bad relay that was stuck and powering the bulb when it shouldn't but it looks like at the most basic level that bulb is wired direct to L terminal of alternator without going through any relay. Already have a new Alternator sitting here .. so will have to try what the FSM suggests.. i guess i can always hook up the new alt without removing the old alt just to see if the behaviour goes back to normal - of course once i've ruled out a short coming from somewhere else so i dont kill my new alt

[badq45t]

I had something similar happen years ago, it turned out that the battery cables were bad. The mechanic put in a new set of cables and that solved it. I do not know about quality of AC Delco didn't know they made Nissan parts but that should be OEM level quality so that shouldn't be failing so quickly. If you have original battery cables they are too old anyways and replace those for sure. As also stated my alarm was for sure causing drains and pulled that fuse years ago.

[FlyingT]

With car shut off, get a digital meter, set it up for checking current amperage, remove a fuse, and touch the meter leads across the 2 fuse contacts in the fuse box. It should tell you the current running thru that circuit. Put the fuse back in. Do that for each fuse and you should find the circuit with the high parasitic losses. Some losses are normal, like the clock and alarm systems.

Also, while the car is off, check the battery voltage. It should be 12+ volts if fully charged. Start the car and retest the voltage at the battery and it should be close to 14V. That tells you the alternator is working fine and charging the battery.