H/D Trailer wire harness

[GMCHORSHAM]

Currently my trailers wiring harness is spliced into the standard tail light harness.
However I have noticed that their is a H/D Red
wire that has been strapped tied in the Engine-
bays bulk head or fire wall on the LH side or in the USA drivers side. I recall reading about a H/D wire designed for trailer harness or Electric brake set up for trailers not sure which.
Can someone through some light on this wire, its
application? How can I use it? Where do I attach it to, Source- Eg Fuse panel or Alternator.
It just seems to me that the previous owner tapped into the rear light harness, possibly not
knowing that this H/D wire was part of this vehicles OEM package for trailer harness.
Any information is appreciated.
Rod.

[diesel65]

That red h/d wire is used for a charging lead to a trailer battery, There should be a h/d blue wire bundled with that red wire, the blue wire is used for the trailer brakes.
You should find the other end of the wire behind the rear bumper, inside the frame rail bundled with the rear harness.
If you should have these two wires then your truck should have the trailer harness installed.
You should also find a wire bundle in the rear of the truck that is not connected and should have labels on each wire to indicate each function. You would not need to splice into the factory harness as the previous owner did.

Good Luck

[GMCHORSHAM]

diesel65, thank you, I should have opened my eyes
before I opened my mouth.
The H/D wire is Red with a black tracer and the
other wire is Black or Blue with a red tracer hard to see the colour in the dark.
Both wires come out at the back and are in the chassis rail as you discribed. Their is a multi
plug where the trailer harness seems to be tapped into, (I owe the previous owner an appology). Cannot get over how small the Harness
wires appear to be !
I guess that's why JK sells a Head light harness
kit if the wire size is the same up front, which it appears to be, thank again.
Rod.