I have a 2006 Silverado. The brake lights quit working, but the third light works. Have replaced the bulbs and the fuses appear good? What next. Already gotten pulled over, that's how I found out!!
Not sure if this is how I post so sorry if it is wrong.

 

Thats exactly what you do to make a post and this seems to happen a lot. The wires that run from the switch to the lights through the bed will rub the insulation off the wire and short it out. My first plan of attack would be to follow the wires and inspect for holes in them to find the problem.

 

Woudl they both go out at the same time and not the third light??

 

Not positive but I believe there is one wire that runs through bed and then it splits for the two lights. I haven't had this happen on my truck but thats what i get from other people's posts. Try looking into those

 

Another place to look would be the sockets that the bulbs plug into. They get corrosion in them at times and make a poor connection to the bulb. Also check foir a good ground at the sockets.

 

Thanks so much, I am a novice but I read most all posts and they didn't address the problem exactly. So thanks to both of you.

 

Try your emergency flashers, if they work, then the wiring to the tail lights and the tail light lamp and sockets are fine (your turn signal and brake lamp are one in the same).
I'm about to trouble shoot the same problem on my 95 silverado. Besides the obvious fuses and relays which you should first check, the other two probable places that neither of us want to go, is the brake light switch and the multifunction switch AKA turn signal/cruz & wiper. The replacement of the brake switch requires you to drop the entire steering column. The replacement of the multifunction switch requires the disassembly of the steering column and a $165.00 to $300.00 part(depending on your buying power). "Northey 87" has a great instructions on "how to change a multifunction turn signal switch in a '95-'98 model". Both jobs require the disassembly of the dash trim.
If you tow, it is advisable to operate your trailer lights through a relay, thus isolating these lights from your multifunction switch and limiting the loss of both trailer and vehicle brake lights simultaneously.


Good Luck!!!