Right turn sinal activates trailer brakes

mramynke · February 20, 2015

2000 k2500 4x4 454 Have had truck and trailer a few years and has always been fine last fall on way home from camping turned on right signal to turn and trailer brakes started engaging with the flashing of turn signal have installed new multi function switch emergency flashers didnt work so it was needed anyway but didnt fix it removed trailer brake controller and trailer wiring harness and using test light it is flashing on brake pedal wire under dash that controler hooks up to, only on right signal not left signal any ideas??

Doug_Scott · February 21, 2015

Did you replace something in between the time it used to work, and when it first stopped working? Generally if you are getting issues between signals, brake lights, and hazard lights you will have either a bad light bulb (filament is broken inside bulb, and has fallen onto the other filament in the bulb creating 'back feed') or corroded light socket. Maybe even a corroded connector on the harness feeding lights at rear, or front of truck.

If it were me, I would first start by removing signal bulbs one at a time and checking to see if it makes any difference. After checking the bulb, and seeing issue is still present, put bulb back in before trying the next one. Make only one change at a time, and reverse the change if condition persists. By not doing it this way, you will likely come to the conclusion that it is something major, when it is actually something very basic.

mramynke · February 23, 2015

thanks for your time. i did have a bad bulb in rear right tail light but problem was there even with tail light disconnected with it fast flashing replaced bulbs plugged back in same problem have looked at wiring havent found a problem

gmtech4 · February 24, 2015

Op , disconnect trl from truck , get a test light and verify if the short is at the plug ,

Find an electrical guy , this is not hard . Except if the Internet is involved

It's in the back of truck or trl

Doug_Scott · February 23, 2015

The signals and brake lights are general using the same wire/filament. Those two circuits can create some pretty interesting issue at times. Never really understood why manufacturers used the same bulb/filament for both brake and signal on rear of truck. If they would have just used a unique circuit for each of the two rear signals, it would so simple to debug/diagnose.

You are going to have to trace the wiring harness from tail lights to fuse panel/brake light switch, signal switch in steering column and the actual flasher unit. I do not know when GM changed over to the "intelligent" flasher unit. The old style flasher can with 2 or 3 wires has been updated to a box with like 7 or 8 wires in it. The multifunction switch you replaced, what are the multifunction's it does?

You may want to try disconnecting the brake light switch and see if that makes any difference. Have you tried unplugging the trailer at the 7 pin connector and check the electric brake wire in that 7 pin connector to see if it still flashes with the signals. If it no longer flashes, you will need to check all the bulbs in the trailer as well. And when checking bulbs, also take a good look at the socket as well.