On the way home, my check guage light came on and my voltage guage was at rock bottom!!! What is going on??? It was very wet out and this has never happened to me before. The last time I seen this was when I had my 1999 5.9L 1/2 ton and the 140 amp relay was shot. I checked it and it was good.. Please help....

 

belt tentioned? or loose wire on the alt. ! bad terminals on the battery! just a few i can think off the top of my head!

 

Batteries good?

 

It charges up to 14.4 volts when cruising but drops way down to 12 volts when idling??? It used to stay pretty much at 14 volts constant..

 

Is the alternator new / good? Mine wouldn't charge and I had it rebuilt (about $100), back to 14+ volts.....this at 104K miles.....

 

I don't know what caused your drop, but I do know on my truck, once the battery has drained down to nothing, the alternater won't start charging again until the battery has a partial charge from a battery charger put on it. Just for future reference... I had a large power wire in the bed that went to my hydraulic lift short out a while back and it drained down so fast my truck died driving down the road. Needless to say, the 3/8 chain that it shorted to was welded to the bed of the truck.

 

Could be the brushes in the alternator. The alternator in my concrete pump would not charge some times. Brushes were worn to short, I lenthened the wire to get more use , that lasted about a month, Then took it to a alternator shop and they replaced the brush set also the copper piece on the armature that the brushes ride on, It was groved and bad also.

 

I just checked her all. The output on the altenator is 12.2 volts at an idle where as it used to be 14 volts. It must be the altenator. Dang NAPA rebuild, it's only 2 years old. The only reason I put on a new on is because this was my first diesel and I bought it in the summer, then winter came. When the heater grid cycle was dropping the volts, I thought something was wrong so I replaced the altenator and both batteries. What a dummy, there never was a problem in the first place. Still the rebuilt one from NAPA should have lasted longer than that. I'm glad I still have the original altenator and the reciept for the NAPA one... Thanks for all the suggestions guys, take it easy....

 

I bought a Napa alternator for my chevy. It was their "gold label", top of the line, "wiz bang", super duty, life time warrenty,Best one. It didnt even last a year. Took it back and the checked it and got a new one for Free.