02 Suburban trailer wiring issue

[WrenchMonkey]

For those who don't know, I've got a 2002 Burb 2500 4x4 8.1L. I like it.

I've got no trailer brake lights. I do have both left and right turn signals. So everything on the trailer from the plug to the bulbs is good, the issue is in the truck.

The wiring diagrams I've found say the trailer brake light signal comes off the third brake light. That is working.

So the signal is getting lost somewhere between the CHMSL fuse and the 7-way plug under the bumper.

I can't find a wiring diagram to show how the three signal (Left, right, brake) gets converted to two (just left and right). There's a "Trailer Brake Wiring" box (assume a relay) on this diagram of the fuse block under the dash, but what's actually there doesn't match the diagram at ALL (see pics).

Additional clue, or distraction: The truck's hazards don't work either. Replaced the flasher, no help. Assume it's the switch and unrelated, but thought I'd mention it.

Any suggestions? Thanks.

[WrenchMonkey]

Going over the manual, I did find a separate fuse for the hazards, "HAZ LP" in the lower right.

I'll check that one when I get home. MAYbe it uses that signal to "flash" both trailer turns at once? I dunno...

[WrenchMonkey]

Originally Posted by Waffle

After you check all the fuses you can think to check, I would suggest getting your multimeter and start tracing power and ground at either end...

That's my issue. One end is the CHMSL fuse and the third brake light. They're good. The other end is where it comes out under the bumper. There, there's nothing.

I know there's something in between; a relay, diode pack, something. I just don't know what I'm looking for, or where it is in the truck, to check it...