All,
I need some of the basics for 73-79 F series lighting wiring:
I recently started replacing light sockets and bulbs on one of my 1978 F-150s.
I got all lights to work.... kinda?
The blinkers work on the right side. The front left blinker works. The right rear does not work. The emergency flashers work, except right rear. When I turn on the headlights,... no blinkers? The blinker indicators on the dash are on? All sockets concerned are three wire types. One wire is connected to the side of the socket and is ground... right? The other two are power wires, one for tailight, the other for blinker/brake,....right? I've cleaned the grounds and reconnected them. I've got a yellow with brown stripe for L.R. and a green for R.R., a brown wire appears to be power for tailights and black for ground.
What's up?
KingFisher

 

Are the marker lights working? I'd check to make sure all the bulbs are making good contact. Double check the grounds up front. I believe the headlights and turn signals share ground up there.
Are these brand new sockets? Or new to you? If you have a DVM you can continuity on the sockets, ( I'll even do it on new ones, just to make sure). Check the voltage on the wiring, before the splices you made, to make sure that's working. Are the contacts on the bulbs clean?

 

Did you look through the tech article? It has step by step instructions for diagnosing problems...

Marty

 

https://www.ford-trucks.com/articles/index.html
The link is in the 4th block of titles.
This one used a 74 wiring diagram.
AL.

 

If you have a problem with the turnsignals when you turn the headlights on, then you have a problem up front in the marker/turnsignal bulbs.

You are right about one wire being ground, and then two hot wires. What will happen is when you have 12 volts on one of the hot wires, it should go through the bulb to ground. If the ground, or the socket is bad, then the 12 volt will instead of going through the bad ground, will find another path, going backwards up the other hot wire, making crazy things happen. That is why the dash blinker lights are on when you turn the headlights on. The voltage from the marker light is traveling backwards up throught the blinker circuit, and making the dash lights burn.

For the above problem, and the rear light problem, you should get a voltmeter or a testlight. You can then probe the wires to see what's actually going on. You can probe the outside of the bulb for the ground connection, while having the other wire from the tester on one of the hot wires. If you get voltage when you touch the frame of the truck, but you don't when you touch the base of the bulb, then you know you have a ground problem in the socket, or the wiring.