I'm working on my son's 78 F-150 and the brake indicator light in the dash is always on (with key), but no brake lights, no rear blinkers, and only the right front blinker works.

I've cleaned all the bulb sockets, cleaned the fuse block and individual fuses, unplugged and cleaned the brake switch located on the pedal mount. I'm honestly at a loss here and could use some direction!

Thanks guys!

 

The brake light on the dash is controlled by this: C8AZ-2B264-A .. Brake Pressure Differential Valve Warning Lamp Switch = 1968/69 FoMoCo Passenger Cars; 1968/79 F100/350, Bronco & Econoline.

 

Do you have a volt-ohm meter? Did you confirm that the bulbs were still good on both filaments? Or in a pinch, you could take the one you know still works and plug it into the other three sockets to see if it's the bulb or still the wiring.
Of course, with a volt meter you could verify that you're getting power to the rear lamp sockets.

Do your hazard flashers work? The same issue where only the one front lights up?
There is no fuse for the brake lights I don't think. At least on the earlier models the power for the brake pedal mounted switch came from the headlight switch and was protected by it's internal circuit breaker instead.
The headlights all work? Running and tail lamps?

Still have fully intact ground wires? One to the engine block obviously (or it would not start) but also need one from the battery to the body, and from the engine to the body.
Doesn't hurt to put one from the engine to the frame either, but the frame is only used for very little in the way of grounding.
However, on some trucks the tail lamps get grounded to the frame. But most (and maybe your '78) go to the body instead.

Good luck.

Paul

 

Yes more checking is needed but note the 4 ways, stop lights & turn signal lights all go thru the turn signal switch.
Dave - - - -