2004 Silverado. Voltage fluctuates from 14 down to 10v, only when it is raining out. Speed doesn't matter. 25mph or 70mph it still does it. Needle does not pulse with the wipers. New battery and alternator. Ground from battery to frame has been cleaned. Battery cables are good. Any ideas?

 

Any noticable problems?are you checking by guage or hand held meter?

 

Couple weeks ago it dropped and a warning came up on the message center, battery not charging. Replaced battery and alternator. Only happens when driving and only when it's raining. All speeds. Have only been watching the volt gauge in the cluster.

 

Ok, but you haven't been left with dead battery? gauge clusters do get issues,but moisture related?start following leads off of battery,give a close inspection,a intermittent short to ground,? a circuit that is on during problem,head

 

Got cut off,? headlights,wipers

 

While it was happening the last time I did shut off fog lights, headlights, ac, driving lights all separately and all at the same time...no change. Turning off the wipers made no difference also. Sanded down ground from the battery to the front bumper, sanded and cleaned area at the bumper also. Next is finding a schematic and checking all the grounds.

 

Right on,that one is small ground wire off battery to radiator support?then passenger head to firewall,harness to frame under drivers side door, harness to box mount at fuel filler door

 

Thanks!! I'll check those out.

 

How is your belt?

I'd say alternator, but you have already replaced that. With it only happening in the rain, I wonder if you might be getting some belt slippage?

 

Okay now I'm really getting frustrated. Truck sat out all day in the 90 degree heat, direct sunlight. Got out of work, started the truck....10volts at the gauge. 20 min drive home mostly highway, no accessories on and by the time I got home....9.5volts. Opened the hood checked battery connections, grounds, starter connection...all looks fine. Let the truck sit for an hour. Went back outside, started it up and 14.5 volts right away. What would the heat effect? When the engine gets up to operating temp the volts drop to about 12.5. I can shut the truck off, count to 30, turn truck back on and boom...14.5 volts. Any ideas?