hello, gm has changed their 07 brake controller wiring. i will include some instructions that should help you. and anything you dont understand please ask me to explain.
Some owners may notice that there is no power at the Auxiliary power terminal of the 7-way trailer connector. Circuit 742 Red/Black is the power feed to the 7-way connector.
To have power at the 7-way connector, circuit 742 must be connected to Stud 1 (40 Amp Fuse) of the UBEC. The wire is taped to the engine/chassis harness under the master cylinder near the I-shaft.
Note: Do not confuse 742 with circuit 242 (Doc ID(NNN) NNN-NNNN which is used to power an aftermarket trailer brake controller. When installing an aftermarket trailer brake controller, circuit 242 must be connected to Stud 2 (30 Amp Fuse) of the UBEC. This circuit is taped to the engine harness between the UBEC and Left Fender. More information on this can be found in Bulletin 06-08-45-008.
Some customers may have questions on how to connect an electric trailer brake controller or where the brake controller pigtail harness is located.
Starting with the new 2007 full size utilities and pickups, there is no longer an electric trailer brake controller pigtail harness.
The trailer brake controller wiring is now part of the Instrument panel wiring harness and the blunt cut wires are located under the left instrument panel, behind the data link connector. There are four blunt cut wires in this harness as described below.
12 Volt power supply (30A stud #2)
Trailer brake output voltage
Stop light input
The Red/Black circuit 242 must be connected to stud #2 of the 30 Amp fuse of the UBEC. This wire is located between the left fender and the UBEC (1). Refer to Trailer Connector/Provision Schematic in SI for document information on the trailer brake control-- Domestic.
the lt blue wire is the 12v brake imput from CHMSL PCB relay which is turn off and off by the bcm, i have included wiring diagram, also check the fuse for CHMSL PSB