HELP!!! charging system failure

B

bigred98

CUMMINS FREAK
Joined
Sep 17, 2012
Messages
3
Hey guys here's the deal, my truck sat for 2 days & when I started it the voltage was low & kept going up & down then bottomed out. I replaced the batteries & the alternator checked out so now I'm stumped. Any input on the issue would be greatly appreciated.
 
The charge circuit is activated by the PCM, it varies the ground to the alternator and is a known failure point.
 
If you took the alternator to autozone it will give you a false passing. Take it to napa. Had the same thing happen to me.
 
I tested the alternator myself by connecting 2 wires to the back of the alternator & connecting them to the battery. It charged when I did that so I'm guessing possible bad pcm?
 
Check the Brushes if they are wore out and barely touching the slip rings that will give you that issue also and that is an easy fix as long as the slip rings are not worn out.
 
Just want to ask the obvious to get it out o the way:

Was the tachometer working when the alternator wasn't charging with the stock wiring hooked up?
 
Everything but the charging system is working. I have already checked everything else I can think of & came up with nothin so far. Guess I'm gonna have to bite the bullet & buy a pcm. Thanks for all the suggestions & keep em comin if yall think of anything else.
 
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