Reverse & Third Brake Lights Not Working

[OleBrownie]

My reverse lights and third brake light have not worked ever since I’ve had the truck, just never got around to fixing it and need to soon. I’m not sure whether it’s a fuse or bad connection; I don’t know how to check and am not very sure where to start a diagnostic. If anyone has any suggestions please let me know, thank you!

[Gary Lewis]

Third brake light?  I'm not sure what you mean as these trucks only have two brake lights.

But on the backup lights the problem is frequently either the switch in the transmission or the wiring back by the lights.  So I'd start by looking to see if the wiring is connected to the switch on the transmission.  Then I'd follow it on back to the lights themselves.

[OleBrownie]

Thank you for the diagram! I think I meant the Rear Cab Light, the one outside the truck above the rear window, bulb looks brand new and I replaced it anyways but does not work.

[Gary Lewis]

You do know that you turn the headlight knob fully counterclockwise to get the bed light on, right?