1998 chevy truck 5.7 liter 2wd. Have a topper on back and when i got it from my brother i noticed the 3rd brake light on my topper is blinking when i turn my left turn signal on? Does anyone know a way to fix the 3rd light on topper from blinking. I just want it to be a brake light. incandescent lights not led on 3rd light.

 

If you’re still needing an answer here….

It sounds like the wiring for the topper light was either tapped into the wrong circuit or there’s a spot in the harness along the frame rail that’s damaged and allowing the left turn signal and topper light to short together.

Trace the wiring from the topper to the spot in the harness where it’s tied into the wiring. If it’s tapped into a yellow wire, that’s the left brake & turn signal circuit. If not, inspect the harness for damage and repair as necessary.

Some trucks had blunt cut wires in place for adding a topper or trailer wiring. Location depends on model year and options, but if yours has it, it’ll be inside the harness either near the rear bumper or along the left frame rail near the cab/box gap. Look for a white wire that’s hot with the brake pedal pressed.

EDIT: Look for a SMALL gauge white wire. There will be a large gauge white wire that’s the ground for the trailer circuit.

If no blunt cut wiring is in place, you’ll need to run a wire into the cab and tap into the white wire at the brake pedal switch.

 

I actually went back and looked at the wiring on my Topper and the Wiring diagrams on my 1998 chevy Truck.. Truck came with a tow package already when my Dad bought it.. CHMLS wire (white wire was located in the wire bundle from the Factory on the truck to the back with a wire for the brake controller and the power for the trailer.. SO i am set to take a 3rd brake light without having to figure how this was going to work.. Did not have to get a Logic module for my truck as the truck already had the wire running from the Brake switch in the cab.. Also if you look at the fuse box to the left of the brake pedal you will see a open connection marked NAT. This also lights up with the push of the brake pedal.. So you could if you wanted to run a wire from that connector back to the back with a 10a fuse and make a 3rd brake light this way too. Thanks,...

 

I recently bought a 98 chevy cheyenne single cab and the 3rd break. Light is out and I can't find any diagrams of the wiring and where those wires run to make shur there arnt any breaks in the wires. Does anyone now where the wires.rum from and to the third break light on the back of the cab

 

The wire actually comes from the brake pedal switch. But on the fuse panel just to the left of the Brake pedal is an option.. Look for the word NAT (a spot blow a fuse or relay spot on the lower right side. It actually lights ups with light/circuit checker when you press the brake pedal.. I have seen others rewire from there and and go back to the 3rd brake light on the topper or where ever. Make sure to put at least a 5amp fuse in the line. I was lucky and had a wiring for the Trailer hitch in the back.. If your truck did not come with a trailer hitch to pull a trailer when the truck was originally ordered then you may not have one.. There should be a bundle under or near your spare tire in the back on the drivers side. a orange, black, and a small white wire. The small white wire is the CMLS for the 3rd brake light.. Some truck have it some dont.
Just a few ideas for you.