whrn i put down the rear window (truck running) the rpms drop turning on the headlights does the same but i turn them off the rpms climb back up. the lights stay bright and the voltage guage drops a little but not extream.
Batterie? wires with bad contact? alternator?
Thanks a million!
David

 

It sounds like your alternator is singing it's death song and is no longer putting out enough amperage. It's putting out enough to run the truck, but not enough to run the accessories too...

 

Thanks WATRD
could this be my problem with the bad idle as well? idles good but every 2-3 seconds it dips and smoths out again. but when i am driving there is no loss of hp or anything.
David

 

It's possible that would cause that symptom. I would have the alternator checked out for function. If it comes back clean, the next culprit I would start looking for is high resistance on a wire, or a bad connection. After that, it's the battery...