No Power to Trailer Plug Reverse Lights

[frazld]

2003 GMC Yukon XL SLT w/ Heavy Duty Towing Package. Towing a boat trailer with surge brakes.
(I know that I can block the surge brakes so I can back up the trailer)
The Normal rear Back up lights work. All Fuses good. I do not have electric brakes or its controller
I do not have power to the reverse light (center pin on trailer plug, light Green Color).
I have checked the under hoof fuse for the Trailer Back up lights (TRLR B/U) and there is no 12v power to either side of the fuse holder. The schematic indicates that it is hot in run or start.
There is continuity between the fuse holder and the trailer connector center pin with 0 resistance.
The electrical diagrams I have seen show that the power to the TRLR B/U Fuse comes from the B/U LP Fuse
thru the Back-up back lamp switch then to the and the VEH B/U Fuse & TRLR B/U Lamp Fuse then to the trailer connector. Seems that that is a straight connection with no switches or relays.
See attached Chilton schematics 12-39 is the main one.

Any help would be appreciated

 

[Scottydoggs]

there could be a back up fuse in the in cab fuse box. thats where the turn signal and brake lights fuses are.

my 4,000 lb boat had surge brakes too. never had a issue backing up.

i did have to drag it down a steep hill once, it was pushing on the truck so hard the brakes locked up. all 4 of em lol

 

[frazld]

Yep checked them all. All Ok.
There seems to have been a mid year change on the trailer wiring.
There Must be a relay some where.
& there must be the correct schematic some where too, but I can't find it.

 

[Scottydoggs]

you need the R light to power a lock up for the trailer to back up?

id just go ghetto on it if thats the case. tap a wire from one of the reverse lights on the truck then run that to the trailer plug. problem solved.

 

[frazld]

LOL. I was considering doing that.
But I like the idea of original with original fuse.

 

[M1Gunner]

So run a jumper from veh b/u fuse to trlr b/u fuse and see if the trlr lights up... if so, then the fault is between the two.

 

[frazld]

So run a jumper from veh b/u fuse to trlr b/u fuse and see if the trlr lights up... if so, then the fault is between the two.

It seems like my only option. Will do this weekend