I have an 04 2500, 4X4, and have added an external fuel tank w/ a remote pump, and a cab protector/ rear window rack w/ it's own bed light and brake light. For the fuel tank pump, I need to tie into a power supply (approx 15 amps), and may need to run a dedicated wire to the battery. For the rear window rack, I would think I need to tie into the trailer plug. Anybody out there have any thoughts or ideas? Thanks, Jim.

 

I would run a separate set of wires to the battery for the pump both neg. & pos. install a fuse or relay for protection.

If your truck came with a bumper mt 7 pole connector you could use one of these to tap the trailer harness (then tie into it for the rack lights):

http://www.etrailer.com/p-V30137.html?search=1

another option would be to get a 4-flat T-plug and tie into that harness as well.

Just don't overload the trailer circuit or bad things can happen..