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1977 F100 3 speed manual on the column
I bought the truck recently and whenever I put it into reverse, one of the reverse lights comes on for about a second and then goes off. The other one does not come on at all. I have replaced the bulbs and it hasnt changed.
Check your reverse light switch. It is at the bottom of your steering column, and visible from under the hood. The bracket which supports the switch itself can get bent, and move the switch to where the linkage doesn't hit the switch when the transmission is in reverse.
My truck was that way when I got it, and the switch was easy to bend back into place. I put the transmission in reverse to see where the linkage would get close to the switch, and then bent the bracket (and maybe loosened the clamp securing the bracket to the column) and moved things until my lights came on reliably in reverse.
Not sure about the one light which ain't working, I would guess that it's either a bad socket or a cut wire/bad connection. Could be a defective bulb too - if they're sylvania bulbs, I'd investigate that first. My driver side backup lamp had a bad socket, but I was able to improvise with the socket and pigtail from a first-gen Ranger.
Thank you! Turns out the switch was causing it to turn on for just a second. I replaced it and checked the socket that was not working. There was a small bit of rust that was causing the problem that I overlooked when I last checked. Now it is all working!