when i crank up the engine in my 2001 2500 she cranks and runs fine when the headlights are on and its sitting there idleing the engine sounds like the ac compressor is kicking on and off, the engine will go up and then it will drag back down and the lights dim a little bit when it idles down, it doesnt change much just about like an ac compressor would but it is off when it does this, anybody have an idea what might be going on? thanks

Your are new to CTD's, I take it?

Perfectly normal. And welcome to DTR.

It is a sticky right at the top of the page.

http://www.dieseltruckresource.com/dev/voltage-drop-lights-dimming-cold-start-t120532.html

thanks, i am glad its normal. yea i am new to the sight and new to diesels i have worked on gas burners for a while.