Need to know how to wire my gmc safari for a tow trailer, wheres the connections? im thinking it is just added to the brake and tail rear light wires but , need to know for sure. thank you

It sounds as though you have either a frayed wire between the brake control circuit and tail/running light circuit of the truck side of the plug, or someone wired the truck side of the plug incorrectly.

Think about it. The parking brake lights come on when the controller is activated. More than likely the tail lights are also.

The tail lights are also going to come on when the headlights are on. This would cause the trailer brakes to be activated IF there is a short in the TRUCK side of the plug itself.

That's where I would personally start investigating, The truck side of the trailer plug.

Hope this helps.

Your truck may have had the factory trailer tow package, but that did not come with a wiring connector in that year. There should be a wire harness under the rear of the truck near the center of the bumper with 7 wires of the following colors/characteristics -

Red/Orange - +12V Battery (Thick Wire) From fuse #8 (40A)
Black/Orange - Tail Markers (Thick Wire)
Light Blue - Trailer Brakes (Thick Wire)
Violet/Black - Backup Lights (Thin Wire)
Dark Green/Red - Left Stop/Turn - (Thin Wire)
Brown/Red - Right Stop/Turn - (Thin Wire)
Black - Ground - (Thick Wire)



Under the dash, the brake controller wiring should be -

Red/Orange - +12V Battery (Thick Wire) From fuse #8 (40A)
Black/Orange - Ground - (Thick Wire)
Light Blue - Trailer Brakes (Thick Wire)
White/Tan - Brake Light sense - (Thin Wire)

Hope this helps.

Thanks Syntax Error for letting us know you figured out the wiring harness was wired incorrectly. It is always a good idea to look up the color wiring standard for the socket and to check the pin positions and what functions .
Sometimes trailers can be wired incorrectly also ?
I wired the licence plate bulb to my brown wire by mistake and this is the brake wire . Took a while for me to figure that one out !

The wires would be secured under the rear of the truck. However trailer wiring is only for trailer lighting. Electric trailer brakes require a trailer brake controller.

Disconnect the trailer wiring and recheck the vehicle lighting. If it returns to normal, then obviously the trailer is the problem. Quite often the trailer plug loses its independent ground and it will back feed thru other circuits trying to locate one. Especially if its a boat trailer, water intrusion can cause havoc on the grounds due to corrosion. The under hood electrical center has circuits intentionally meant to be used for trailers. You CANNOT just jumper into the rear lights of the truck (tail, signals and brakes coming from the tail light connector). Because it uses a multi-function switch, the brakes and signals are actually the same circuit, and have to be wired separately for a trailer plug to operate.

Towing and hauling usually means it has some options to make it easier to tow or haul. In this cas it will have a hitch and the plug for teailer lights... It will have a few other extras as well maybe even heavier brakes but no electric brake control or wiring in the fron for it. Sorry...

CAV CIRCUIT FUNCTION 1 Z13 12BK GROUND 2 B40 12LB TRAILER ELECTRIC BRAKE OUTPUT 3 L76 12BK/OR TAIL LIGHT (Trailer Tow Relay in PDC) 4 A6 12RD/TN* FUSED B(+) (40A, Always Hot, F8 in PDC) 5 L63 16DG/RD LEFT REAR TURN SIGNAL TRAILER TOW 6 L62 16BR/PK RIGHT REAR TURN SIGNAL CONNECTOR 7 L1 16VT/BK BACK-UP LAMP FIGURE 1: 7-Terminal Trailer Tow Connector

Here's one
CAV CIRCUIT FUNCTION 1 Z13 12BK GROUND 2 B40 12LB TRAILER ELECTRIC BRAKE OUTPUT 3 L76 12BK/OR TAIL LIGHT (Trailer Tow Relay in PDC) 4 A6 12RD/TN* FUSED B(+) (40A, Always Hot, F8 in PDC) 5 L63 16DG/RD LEFT REAR TURN SIGNAL TRAILER TOW 6 L62 16BR/PK RIGHT REAR TURN SIGNAL CONNECTOR 7 L1 16VT/BK BACK-UP LAMP FIGURE 1: 7-Terminal Trailer Tow Connector

I take it the blinkers and brake lights work ok when not hooked up to the trailer? If yes, then the wiring to the tow hitch is not hooked up correctly. How many wires to trailer pig tail connection? U can have up to 7 depending on what you tow. Check to make sure these wires are hooked up from the truck to tow plug correctly: 7 wired---
brown-Rt turn and brake light, yellow-backup, white-ground, blue-electric brake, green-tail running lights, black-battery charger, red-left turn signal and brake light. Let me know if u have something other than 7 wire, I'll get the wiring color and source info for u.

exactly what does it do? please explain what happens when you press the brake turn on the light than brake signals ect.....