charging issues

[cupp_cody]

On my 1989 c1500 with a 4.3 i have changed the alternator and had it bench ******. mit will charge fine and the all of tje sudden on my voltmeter it will drop. so i thought the guage was bad. i tested it with my voltmeter and it says 11.6 volts. and then it will run nornal and be fine. does any one have any idea what would cause this? Exciter wire? I have bern having a lot of trouble with this. I've cheacked my conections and grounds.

 

[HotRodPC]

Are you noticing dimmed lights or anything like that when the voltmeter is reading 11? How about starting issues? Having any?

An alternator can test just fine but be bad. These bench testers just test output and they're not real world tests. Could be the volt regulator in the alternator and it working fine when cool, then warms up and screws up, could be dirty brushes, worn armature making an intermittent issue, could be a diode or a rectifier bridge which will not show up as defective at all on a bench test. So, you've verified all your connections and cables are good. You've confired the low voltage with a test tool at the battery and it's matching what your dash gauge says, so that says your wiring to the gauge is accurate. It if starting OK when the battery is at proper charge, and lights are dimming when you see the gauge dropping, then it's now safe to assume the alternator is bad or going bad and on it's way out.

 

[350runner]

Mine did that b4 I changed my fuse links at the starter. Good luck