This 2001 Chevrolet Silverado came in the shop with the complaint of no stoplights. First I confirmed that none of the stoplights were working including the CHMSL (center high mounted stop light). After this I went to the underhood fuse box because the manufacturer has made diagnosing the stoplights very easy at this location. By going to the red, 10 amp, vehicle stoplight fuse, #17 and checking for power while some pushes on the brake pedal I can tell easily if the stoplight switch is good and I do not have to lay under the dash to do it. I identified the fuse location using the legend.
This one was really easy because when I located where the fuse was supposed to be I found that it was missing. I installed a new fuse and tested both sides for power while someone depressed the brake pedal. I found that the owner had been swapping fuses trying to keep his power outlet working for his cell phone charger.
If I had found power on one side of the fuse but not the other it would have indicated a blown fuse. If I had found no power on either side with the brake pedal depressed I would have suspected a faulty stoplight switch or no power to it and more testing would have been needed.
Luckily, the power supply fuse for the stoplight switch is the yellow, 20 amp fuse, #14 is right above the fuse I was testing. Testing here would have shown one of two things. Power on fuse #14 with no power on fuse #17 would indicate a faulty stoplight switch. If fuse #14 had been blown it would have indicated a short between the fuse and the stoplight switch and back to fuse #17. Also a blown fuse #17 would indicate a short between the fuse and the rear of the truck.
Hi 99Silverado,
Since you mentioned that you checked the CHMSL fuse, I am assuming that your truck is the new body style. If so I would recommend checking the wiring at rear lamp buss block. It is located at the rear of the vehicle near the spare tire area. There should be three light blue stoplight wires there. One is input from the vehicle stoplight fuse and the other two are outputs to the stoplights.
Hi Sparky! My 1999 Silverado is without brake lights including the cyclops. The fuses are good, and I’m getting power on both chmsl and stop light fuse. Also, I have working interior lights, headlights, taillights, turn signals and reverse lights. At the trailer adapter there are 4 broken wire and they’re coming from the adapter. 1 – black and 2 – white and 1 – red. When I put a test light in one of the light sockets, I get power with the lights on but not when I depress the brake pedal.
Thanks,
99Silverado