Trailer wiring

[TKRESS1]

I installed a new rear wiring harness on the M37 and all lights on the truck work correctly but I have no power to the trailer plug on the truck. I checked my M101 trailer by hooking it to my M35A2 and all the lights work correctly. So I check the ground and all splice connections and all is good. My questions is the wiring hanging in this picture what does it do? Is this how the powers gets to the trailer plug on the truck?

 

[Storm 51]

The manual has the wiring diagram. If you don't have the manual, I can email you a copy of the wiring diagram (pdf copy) if you PM me your direct email. You might also check the M37 manuals in the manual section of this site. It looks like you are looking for wires 21-A, 24, (& 24-A) 23-A, 22-460-E and 22-461-D. These should be on the truck side of the harness.

Good Luck! The wiring is actually pretty easy if you have a stock harness and a wiring diagram.