Thanks BenK.
I've been looking thru the service manual and I had hit the same pages you uploaded in your thread. I still haven't found exactly where the brakes combine with the blinkers for the tow harness, but I've come across a few things that let me think I'm getting close.
On page 8A-110-6 (box at top) "WIRE LEADS ARE TO BE SPLICED TO TRAILER WIRING HARNESS OR ATTACHED TO TRAILER WIRE PLUG". I think this backs up what you mentioned - that they are (or were) spliced (somewhere).
On page 8A-202-9 there is a description of a 48-pin plug that is said to join the steering column harness, and that 48-pin plug has the white wire (pin A1) for TCC/StopLamp Switch for Suburban and it also has the dark green wire (pin E6) and yellow wire (pin E7) that are the correct colors that go to the tow harness.
So, would it be safe to splice that white brake switch output wire into the blink wires for the tow harness ??
Many thanks!
Marty
