Help !! I have just purchased a new ( to me ) 07/classic 2500 Dmax to replace my 01/8.1/ally...the problem starts with moving my Tekonsha P3 controller to the new truck. This should be plug and play, as it was on the 01, as far as I can tell. But when I put it in the new truck, as soon as I turn on the ignition switch and the auto sensor turns the lights on, I get 2 volts ( also 2 amps ) applied to the output to the trailer..I checked this not only on the controller, but also on the output pin on the bumper plug....this is with no brake pedal applied.....if I force the auto sensor to turn the lights out, the applied voltage goes away but then I don't get any voltage when the brake is applied. The manual lever applies the brake ok all the time ( but it doesn't get its power from the taillight circuit ) It almost seems like the brake pedal portion of the circuit is getting its power from the wrong source (Headlight Circuit instead of taillight ). The original owner never towed anything, so I am not sure if the harness was installed correctly in the first place. Just to double check myself I took the P3 out and put it back in the old truck and all is as it should be ( no voltage at trailer brake pin with lights on and no pedal applied ) According to the manual there is no additional fuse to worry about with the dual battery setup....anyone out there ever heard of anything similar ??? could I be missing something like a bad relay??? It doesn't seem like a controller problem if it works fine on the old truck....could it have been wired wrong from GM, or is this whole harness just a series of plug ins from end to end ?? Lots of knowledge on this forum...hoping someone has an Idea ( its getting cold up here in BC and I can hardly wait to head south ) Thanks for reading.

The harness pin assignment changed in '03. Fear not, the general has bulletin on that. Start on the right side of page 3.

http://www.gmupfitter.com/publicat/bull/bull57.pdf

heymccall,
WOW, that was easy. Thanks for your quick and accurate response, I can now go about repairing the hole in the drywall where I have been banging my head. I can't believe I spent all day on that thing !!! It all makes sense now when I look on line and see a different part number for post 06 trucks. I will swap the pins tomorrow and see what happens. I wonder why they changed them ?? Thanks again.
Grant Simpson
Victoria B.C.

heymccall,
I wonder why they changed them ??
Grant Simpson
Victoria B.C.

Geez...Even I know that one. To subsidize the drywall industry:rolleyes:

i did that with my dads 04 gmc. we took the harness out of my grandpas 02 and i had to switch a wire to a different pin and then everything worked great

Couldn't wait till morning to see if it worked so, out with a flashlight..put it all back together and low and behold, IT WORKS...I got a bit confused where GM said to swap the two wires, as the Tekonsha harness didn't have a wire for "controller illumination" , so just went from "A" to "D" ( there was nothing in the "D" before ) Thanks again "heymccoll" for all your help.....hopefully someone else can read this and not spend all day at it !!
Grant

( also note that Tekonsha color code not the same as GM !! )

Praise the Lord just spent two hours killing myself as to why my 02 harness wasn't working with the 07. parking lights were flashing etc Thank you for this thread!

I wish I had known this...I ended up getting the "upgraded" harness which worked perfect but now I have this old one...Oh well, live and learn.