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Electrical

I have a 1989 Ford F-150 truck and I’ve noticed that the right rear brake light and turn signal is not working, but the tail light is. I changed the bulbs, thinking that was the problem, but this did not correct the problem. I just had the transmission worked on and I was wondering if the mechanic might have knicked a wire. What should I try?

A first step would be to examine the socket for heavy rust or corrosion. Then test the contact point with a voltmeter to ensure it is delivering +12v. If OK, next trace the ground.

I seriously doubt the transmission work is any any way responsible for this problem.

How did the electrical contact in the bulb socket look like? can you test for the presence of voltage at the contact point (test light,multimeter).

I would not think the trans work is related but you can get under there and look.

If the contacts in the socket are ok then the flasher unit is most likely the trouble. The brake light circuit runs through that also.