1985 F150, 302 carbed,

I am having issues getting my passenger side brake light to work. It was intermittent for a while and now seems to have stopped completely. Everything else with that bulb is working such as the tail lights, and signal lights but it will not come on with the brakes (lower reverse light is working as well). Thought I would ask before I tear into this completely in case you guys have some simple tricks that I am missing. Here is what I have done so far:
- Switched bulbs with the drivers side and it still didn't work on the passenger side so the bulb is good
- Checked fuses and they seem to be fine if I was looking at the correct ones
- Using a test light I wasn't getting any power to that socket with the brake held on. (did this with the drivers side as well and it had power)
- Followed the wiring under the truck up until the engine bay and I don't see any signs of obvious damage. It is encased in wire loom up until the rear axle area and then tightly wrapped the rest of the way. The wiring is original so there is always a chance it cracked somewhere in there. Getting the wrap off is not going to be a fun job.

Any advice is appreciated. Maybe there is a ground wire somewhere that would interfere with the brake light or something else connected with it. Wiring diagrams would also be helpful. There are 3 wires going into that socket and I am not sure which one is for the brake light.

 

Turn signal switch is all I can say.

Why you ask?
Remember the switch works the right / left turn when the brake is not on.
Now have that same right / left light on and hit the brake what happens?
The brake light on the side the turn was on, the brake light turns off and the blinker still blinks.

Now before I would go replacing the switch I would try a few things first.
You can try flipping the lever left & right a bunch of times.
Spray some electrical contact cleaner & lube in there and try flipping the lever left & right a bunch of times.

If all that does not work then replace the switch.
Dave ----

 

Your problem will be the turnsignal switch. It's job is a "traffic cop" for the turnsignals and the brake signals for the rear lights. When it's in the center, it puts both rear brake bulbs on the brake pedal switch wire. When you move the turn switch to the left, it takes that rear driver's side bulb off the brake switch, and puts it on the flasher wire coming from the flasher. It leaves the right side on the brake switch. It does the exact opposite when the turn switch is moved to the right. The rear turnsignals use the same filaments and the same wires as the brakes, so the reason for the complication at the turnsignal switch.

 

Look on page 76 in this link. You can see the switch, and it's complexity. You can also see the flasher signal and the brake pedal signals coming in on either side ( I forgot the hazard flasher also).

Turn, Stop, & Hazard Lamps - ???Gary's Garagemahal

 

This is the type of news I was looking for because believe it or not I have a brand new turn signal switch sitting in the garage waiting to be installed. With my current one I have to hold it both ways to work and even then its hard to get it in just the right spot to activate the blinkers. I never thought that they would be connected right there so thanks for that info. This would also explain why that brake light was working sometimes. I'm sure if I wiggle the turn signal switch a bit it would put it back into the correct spot to work the brake light. Time to put off swapping out that switch!
Thanks again.

 

Let us know how it works out.
Dave ----

 

Got the new switch put in today and everything is working again. Not a bad job to do other then struggling with unplugging the harness for a bit while my head was crammed under the dash haha. Thanks everyone.