Freightliner classic Left brake light won’t work classic

Check your wiring, ground wires, etc.

 

Well, you could unplug the brake light pigtail/harness and put something on the brake pedal and check for voltage to make sure the signal is getting to the light.

If the signal is not getting to the plug then you got to find where it is getting to/ or supposed to come from, and see where the disconnect is. I doubt it’s a fuse because your other brake light works. Have you tried your other tail light in place of the bad one? Because u know the other one works. I recently had a trailer tail light brake go, on the left side. I replaced it with a spare. Still no go. I got into cutting wires and resplice’ing pigtails and my father was like did you try your other light in that place. Well, turns out my spare was bad too.