battery/alternator or fuse/relay problem

[Fabian]

my dad was messing with a after market stereo (connecting it) which he did then the next day he drove the car around in the morning it was fine then in the evening it the car died on him i figured out his battery was low so i got him a new one the car ran fine a few days later it died again he took it to the shop they said the alternator was fault now we went through two alternators (remanufactured ones) and the car battery still wont charge i tested the alternator with a voltmeter and sure enough its not charging the battery but its basically new does anyone think it could be a fuse, relay, or even wiring the cars a 1990 dodge dynasty any input is greatly appreciated thanks

Topic

[Wayne]

Before bothering with a diagram or the like, test voltage on the B+ terminal with a DMM if you can get to the back of the alternator (to check before the fusible link that protects the rest of your electrical system from a faulty alternator or any short on that line). Obviously be careful, as you will need to start the car. Or you can verify with a continuity test from the B+ terminal and the battery terminal, either way.

Assuming the alternator’s ok, there’s only a few reasons why it’s not putting out. Either the exciter isn’t getting 12v to create the magnetic field, or the battery terminal isn’t getting the output. Exciter line will be fused, in newer cars it’s on one(if more than one) of the computer’s fuses used, but in that it’s likely part of a secondary micro-controller, so yank and check the fuses in the engine bay’s box (faster than looking it up from a diagram). If you still got nothin’, I’d check all contacts, battery first, then the harness going to the alternator, as it’s the likely suspect for corrosion causing the issue. Eyeball the pins on both the connector(usually 2 or 3) and the alternator itself to make sure nothing’s bent, broken or corroded, use electrical contact cleaner from a local parts store if you see any. After that, you’ve just got the engine/alternator ground to verify if you can verify power to the exciter line when the car is running.

[John B Kobberstad]

Was this a problem before the stereo installation? Try removing the stereo and see if the problem persists. If it doesn’t then problem may be with the way the stereo wiring was done.

[Fabian]

This was not a problem before the stereo was connected I already disconnected it and it still persist I will try sum of the suggested test above and inform u guys of the results thanks again

[EricTheCarGuy]

You may have a parasitic draw because of the new stereo. These videos may help.

Alternator video

Parasitic draw

[Wayne]

I’m all for the most logical cause, but are we reading the same thing here? He’s stating the alternator is not putting out. To me, he’s saying the battery voltage is not increasing when the car is on, from when it is off. Meaning something charging system wise is FUBAR. Possibly caused by the install, or triggered by it, but not a parasitic issue.

[dreamer2355]

Great posts above. I would revisit the install or even disconnect the stereo as already stated to see if the problem disappears.

Using a DVOM and checking for a battery drain would be the quickest method though.

[Author]

Replies