04 z71 tahoe, The brake lights suddenly stopped working, all 3, left, right, center top. I checked all applicable fuses. Still good. I noticed if I plug a tester in the trailer harness, it indicated the connection for the harness brake lights is working. If all the other lights arent working, but the trailer harness brake light connections are working, could it still be the Brake Light Switch? Does the BLS control/affect the harness brake connections? TIA

 

the stop lamp switch feeds into turn signal/flasher module located in the left ip fuse box. from there is feeds separately to the truck and trailer light feeds.
which fuses did you check? the fuses in the left ip fuse box? the chmbl 10amp and vehicle stop fuse 15 amp.
b4 you get to involved, its never a bad idea to check for power to the bulbs. on old vehicles that never get periodic bulbs checks...it possible all 3 bulbs are blown.

 

Thanks for the reply. I checked the fuses circled in red, both int fuse box and under hood. I will check the power to the bulbs. The bulbs all going out at the same time would be especially odd since I got an inspection sticker 3 weeks ago and I know they were all working then. So if I’m reading your reply correctly, the brake light switch DOES INDEED control the power to the brake light connections in the trailer harness. Is that correct?

 

you are reading it correctly
if you can check the 2 fuses I mentioned...are they powered with the brake pedal pressed and not powered with the pedal released?...this would verify a good brake switch input. I haven't checked the diagrams but I assume that is how they work.

 

Today, I’ll check to see if those fuses are powered when the brake is activated. I’ll let u know thanks for the insight.

 

Checked the power at the fuses. Power is on, damnit. Check each bulb. One bad, one just needed reseating. Got a replacement coming for center top. Checked the old one for continuity, tested bad if that means anything. Should always do the obvious first. Thanks again.