Location of the brake light switch for a 2000 GMC 3500

Hi Saddleback,

The brake lights on the trailer has been fitted with new tecknology. As soon as you apply the brakes the trailer brake lights will flash. This is let the cars behind you know that you will stop and they must keep their distance.

Here is a picture of the brake light switch. Also at this point just buy a new connector and splice it on, much easier.

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.

Does it have a trailer hitch and wiring? If so, check to make sure connector is not shorted out and double check your fuses and/or replace fuse. It may look good but I've seen some that were burned out of inspection view. You might also want to trace wiring back to brake lights, just in case snow or build up pull connectors apart.

Should be switch clear at top of brake peddle if I remember right it looks like a tube facing fire wall

sounds like a ground problem on the trailer

check the fuse and maybe adjust the rod coming to the switch youdoit.com

test your brake switch located on the brake fulcrum. you can unhook the wires and usea paper clip to connect the two wires together if the brake lights come on then replace the switch, if it does not come on and the bulbs are ok then replace turnsignal switch.

I found the problem. Talking with a technician from the controller company, we determined that it was a fuse problem. I found that the fuse to the CHMSL was blown.

Back in the rear of the truck up under the tail gate area the wires there always seem to corrode and loose connection.If you have ever had a trailer hooked the spot where they connect to the truck wiring.Those sometimes come loose or also corrode.That really the only spot they have problems If you have a test light go back to where the wires are connected to the rear lighting and test for power there.You should be able to find the problem there I hope this helps you.And Have A Great Day!!!!!!!

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