Recently bought what I've been told is a 1976 F100, but appears to have some 1978/79 items. I have a weird issue: the turn signals in the rear work fine, as do the parking lights and brake lights. All bulbs look good, nothing blown. When I turn on the hazard lights, only the rear passenger light activates. Everything else is dead. What in the world would cause that?

 

There are two of these under the dash above the fuse box, one is for the turn signals and the other the flasher. I would change that, its most likley it.

 

You could actually swap them and see if your flashers work, then you would know if it is it or not.

 

Do you mean the rear passenger light actually blinks or just turns on?

 

first thing I did was check the bulbs, they are all good. Next thing was to replace both flashers. When I turn on the left turn signal, the left light blinks correctly. When I turn on the right turn signal, the right light blinks correctly. When I apply the brakes, the brake lights come on correctly. When I turn on the parking lights, the rear parking lamps work properly. When I turn on the hazards, the only light that comes on / does anything is the passenger rear, and it flashes. No other light on the truck comes on or flashes when the hazards are on.

 

Pull the flashers, check for corrosion. Swap with other one, see if it works.

 

already did, wasn't the issue (even tried it again with the new flashers)

 

Did you check the corrosion on all bulbs in question? I would invest in a bottle of contact cleaner DeOxit is a good one.

 

yep, checked that, checked the grounds, etc. They all work except when I put on the flashers. I wonder if the flasher switch is going bad, or if the column wiring is messed up (getting the impression that this truck is a hodge-podge of years)

 

Can you get access to the flasher switch? Spray cleaner in those contacts and work the switch a bunch of times. Wiggle it a bit. See if the don't come on.

 

sounds like the turn signal switch is screwed up