Same issue as 4x4HEMIrig had:
Made a point of searching the threads on tail light problems first.
'04 1500 5.7L
Currently: Neither the left or right brake light works, the cab bake light does.
This started out as only one brake bulb gone bad, which I was going to fix today.
Decided to clean the throttle body, top the fluids, clean the battery posts, and spray down that power steering valve with the steel lines, with a bunch of brake clean, to find the leak in there.
Somewhere in the process I lost my brake lights. May have sprayed something else with the brake clean .. ?
Six pin brake switch showed one post constantly hot at 12v, the next pin open, or hot at 12v if I let out the plunger. Changed it for new anyway.
Rear bulbs are good as far as I know. Alway made it a point to sandpaper down the contacts and apply a touch of grease with a bulb change, and never had them all go bad at once.
Rear plugs to tail and brakes show:
Five pins; two on the left and three on the right.
Bottom left pin is black ground and both sides meter to the body at 1-2 ohms
Top left pin is neutral with respect to ground.
Top right pin is +9.5v +/- to ground
Middle right pin is +9.5v +/- to ground
Bottom right pin is neutral to ground.
Tail lights work, blinkers work, haven't checked the reverse light, but know it was working the last morning I drove it.
This is all I know at this point. I've read a good number of threads on this, which had some good advice.
Trying to think back to what I could have done to turn one bad bulb into no brake lights.