High Voltage after washing truck

A few months back I assumed my alternator was going bad as my scan gauge was showing voltage fluctuations from 13.9 - 18.3V! My battery light would flicker as well. So I got my factory alternator rebuilt and it was good for a few weeks. But as soon as I washed the vehicle the voltage once again was fluctuating all over the place. It seems to be a loose connection that shows up when the engine bay is damp. I let the truck dry out good and the problem is gone, but as soon as it gets wet the problem returns. I checked all the grounds and everything is tight. Has anybody else had an issue similar to this? Just not sure what else it could be.

 

Weird

I would think loose connection would cause an undervolt problem.

I think the alternator is fielded by the engine computer. Field circuit may be shorting to ground on the jegative side of the field circuit causing it to go to max volts.

Or

It just simply has bad parts and the water has nothing to do with it. I rebuilt both alternators in my CUCV and one would do the same thing while driving. Blip the charge light and make my voltmeter go crazy. Just had a faulty regulator out of the box. But I'm almost certain that wouldn't apply here. Probably wiring issue.

 

It has to be the wiring from the alternator that is defective. I'm going to monitor the voltage with a meter and spray water with a hose over all over the wiring harnesses within the engine bay. I need to get a wiring diagram for the alternator cct.

 

Sounds like a bad voltage regulator to me. You say you got it rebuilt. They should have replaced the VR, but did they?

 

The voltage regulator was replaced, they gave me the old one back. This problem only arises when the engine bay is damp or wet, leading me to believe its a wiring issue. Can anyone point me to a wiring diagram for the charging system?

 

Problem Solved!! So it turned out to be the white wire from the alternator connector back to the fuse box connector was corroded. I monitored the voltage while I sprayed water on the wire harnesses and within a couple minutes my voltage started varying between 13 - 18V. I checked the resistance of the three wires leaving the alternator and the white wire was over 10Kohms and constantly changing. I took apart the wire harness and found the white wire cracked and green with corrosion, replace the wire and everything is good again!

 

Good find. I would bet that's the Alt-S circuit wire for voltage regulation

 

That's correct, it's the 'S' wire shown below. Not sure how this could even happen as it's protected in wire loom.