Dad borrowed truck and wired 7 pin trailer harness. Lights worked on truck/trailer for use but upon return the turn signals didnt work. Hazards and running and brake lights did work. Replaced TS flasher and Haz flasher. Still no signals. Pulled steering wheel and replaced turn signal cam only, not whole switch. Now no brake lights, no rear hazards or turn signals. Losing my marbles trying to follow schematic and using test light and mulit meter. All bulbs and fuses are good. Running lights and head lights working as well.

Any suggestions appreciated

 

Obviously something happened when the signal cam was replaced. Possibly a loose connector? I would take that back apart. I don't know if you realize it or not, but the brake light wiring goes through the turnsignal switch and the steering column wiring.

If you get back to where it's just the signals not working, I would check for voltage on one of the flasher socket pins with the keyswitch in run.

 

Flasher sockets are both 12v and the start clicking when I touch the Test light to the connectors at the T/S switch. Prior to replacing the cam I ran this diagnostic (Turn and Stop Lamp Diagnosis for 70's Ford Pickup .: Articles) and again afterwards. Same result, no continuity for the turn signals. I can only assume that something now has happened to the brake lights and hazards also. When I press the brake pedal, I find power in the R/Bk wire at the stop switch, T/S switch, C-305 connector under dash, but then I lose the R/Bk wire at the firewall. Any idea what happens to it there?[/I]

 

The red/black wire that leaves the brakelight switch goes up the steering column and feeds the turnsignal switch. It goes through the turnsignal switch and comes out into two different colored wires that go to the rear lights. If you have another red/black brake signal wire going somewhere else, that's going to be for a trailer brake controller or some other device that needs the brake signal. The raw brake signal wire is not going to go to the rear to the lights.

I believe the red/black stop wire exits the turnsignal switch as a green wire(pass side rear) and yellow/black(driver's side rear). If the turnsignal switch is good, when you hit the brake switch, and the turnsignal switch is in the center position, both the green and the yellow/black should become hot.

 

I got ya beat! My problem is when I turn my turn switch left or right the front turn lights work but the rear tail lights both flash together. Also only when turning left the third brake light flashes with them as well. Also the front left turn light goes and stays solid when stepping on the brakes. All three rear brake lights go solid when brakes are applied even with turn signals on.
Is it a short somewhere? I replaced the Multifunction switch and flasher relay , checked fuses and bulbs.

 

You have some wires melted together or miss-wired somewhere. The first place I would check is a added trailer plug in the back.

 

Ya the previous owner had a fire in the engine compartment also there is no trailer harness attached but lose wires hanging down. Might be easier to just replace the wires than try to find the short. Don't know how though.