Brake lights do not work

Some people wire trailer plugs differently. If the plug is not wired differently than yours, make sure the tow ball is clean. No rust. That's where the trailer gets its ground from. Usually they will work if thats the case, but not right. I can't remember what the wire colors are right now. Go to etrailer and look up the diagram.

so then if you unplug the switch on brake pedal the brake lights stay on if so check operation of the hazzards and turn signals could be a short in the turn signal switch or flasher unit also check for pinched wires around third brake light and tail light wireing does your car have trailer hitch ? if so check the trailer plug wireing

change the brake light switch and when stationary put in neutral with hand brake on instead of sitting with foot on the brakes

if have trailer hitch - check for bare wires shorted together, if no trailer hitch look inside left frame rail at tail end- harness should come from front of truck to this point then cross over to right side- look for a cut or bare wiring again

None of the lights work? Reverse/brake/tail lights? If it's all of them, then suspect a module that controls the lights...if it's 1 or 2, check the brake switch @ the pedal. Do you have a trailer hitch w/a wiring harness? That may cause issues.
TD

Sometime around 2000, GM started putting trailering pre-wire harnesses in the vehicle. Your truck may have this harness built in and would greatly simplify brake controller installation. Look under the glovebox and see if there is a wire harness tied off. There will be four wires in this harness, which should be run over to the steering column to use it. Most trailer brake controllers are compatible with this harness.
The four wires in the harness are: Red, 12vdc; black, ground; blue or purple, brake pedal; and brown or white, trailer brake wire to seven pin, four pin, or five pin connector at trailer hitch, if your truck came from the factory with a trailer hitch.
If you are adding the hitch and do not have the four wire harness, the under hood wires from your brake controller are Red, connect to one of the studs under the distribution box cover (the distribution box is on the driver's side against the firewall. Underneath the cover are two large threaded studs which are hot from the battery all the time); and the other wire from your brake controller would have to be run the length of the truck along the frame, tied off in several places, to the trailer hitch connector on the bumper. Follow the directions that came with trailer hitch wiring connector to connect this wire to the proper pin in the connector.
If this has helped you, great, and please remember to vote/comment.
Good luck!

wires on truckhave a feed ,are they connected correctly??

If you have an aftermarket trailer towing plug on it, that's where i would look first. Something is shorting out in there, or you have a broken wire or ground somewhere. Proabably near the back where gravel stones can hit.

The brake lights (excluding the 3rd brake light) go through the turn signal switch. It's possible there's a bad connection in the switch causing your symptoms. I would rule out the brake switch on the pedal, considering the third brake light works. Locate a wiring diagram for the brake light circuit, follow the wires into the steering column as far as you can and verify it's getting power up until the turn signal switch and verify no power is coming out of it. Once that's determined it's time to replace the switch.

If the brake conrol iis activating by manually moving the slide lever but not with the depression of the pedel the problem is no brake signal you need to have power to the red wire coming into the brake control. One of the two white wires coming from the brake switch is switched power and you could wire in there. A test light and time will fix your problem.