Last night me and some of my buddies got in my truck and took off. The truck had been sitting for a couple of days. Igot out of the parking lot and slowed down at the red light and lights got dimm and voltage dropped well below normal. almost immidiately it went back to normal. It did it couple more times as we stopped at other red lights. Whats going on?

 

Is the weather getting cold where you are?
It was probably the intake air heater turning on and off.
Normal condition. It draws huge amperage and the alt can't keep up at idle. Don't worry about it

 

thanx! makes me feel better. also went to local dodge house before got to rooom was going to have them check alternator, but they gave me the same answer you did rabbler. and yes getting colder 'round here. but not "winter cold" on regularbasis, yet!

 

i take that back it dont make me feel better. seems like there should be some way to keep such a draw from happening?

 

Don't worry it won't kill you battery. I agree it's kind of annoying and a bit unsettling at first but I don't think there is a way around it. It's common annoyance to most diesel engines.
The engines need the extra heat from the air intake during warm up and decel otherwise you get incomplete combustion and white smoke out the tail pipe.