Working on my co-workers 1990 Plymouth Laser w/turbo. My coworker was told that his altenator was dead by a mechanic that tested it. I picked up a new one and installed it he drove it for 1 1/2 days and the battery died and it won't start. When I put the altenator on, I did a volt metre test and while the car was turned off, the battery was 12.2 volts. We started the car and the voltage went up to 13.1 volts at the battery. Any ideas on something we can check? I do remember when the car was running, I lifted the positive( I think) (it kept running) off and put it near the positive terminal and it was making tiny sparks. Thanks for all replies! ( I meant to say the battery is not new but will hold a charge for a couple days with a battery charger)

Check all drive belts and turn on all accessories in the car and check voltage at idle and at high rpm if the car cuts off with all accessories on ( headlights wiper etc) check an electrician also change all relays they can remain closed causing a drain in current

Regulator is dead. Has to be higher than 13.1 V.

You either:
Got a DOA alternator (alternator or regulator problem)
Have a bad firewall connector to alternator

-or-
You have a loose cable like the battery cable which is not tight and it fried the alternator.

That is impossible as the ground is from the battery and the current does not return to the alternator, I can only tell you what to troubleshoot so check all leeds and belts make sure they are tight and clean all grounds on the car.if nothing works find a alternator with higher amperage as the engine may be overworking causing the rectifier in the alternator to die out.

You must get reading between 13.5v to 14.5volts

This link may give you a few ideas:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-10.html#post1973613

Well it turned out to be a faulty altenator... Put a new one in and 14.1 charging volts... thanks guys!