Hoping someone can help out with my electrical problem(s). So here is what is going on with a 1978 F250: I keep burning out the left tail light bulb (brake and turn signal), all other lights work great including RT tail light bulb (brake and turn), when i switch the fuel selector switch the dash lights for the turn signals blink once as the switch is flipped from Main to Auxilary and i've noticed the left turn signal blinks slightly slower than the right side (I'm using an electronic flasher unit - maybe slower flash is due to burnt out LF tail lamp bulb? Also the fuel guage does not work for the Main tank but does work for the Auxiliary tank. I have not checked the sending unit yet and this problem may or may not be related to the above problems. Anyone have any ideas of things that I should check? The complete wiring harness was completely cleaned up when i redid the truck and everything looked to be in excellent condition. I'm stumped.

 

This sounds like a laundry list. Lets look at these one at a time. For future posts, please try to use some more punctuation and general sentence structure to separate things out and make them easier to read.

As a sanity check, remove the bulb and check the voltage at the socket with a multimeter while a friend pushes the brake pedal. Report your results. Also confirm that you are using 1157-style bulbs.

Look behind the back of the heater control panel to make sure nothing is caught in the back of the switch, particularly with the heater control panel illumination pigtail. The dash light circuit is a BLUE with a RED stripe wire.

If you're using an electronic flasher, the bulbs shouldn't blink any faster or slower with one bulb burnt out. That only matters with thermal flashers. Are you sure this is an electronic flasher? As a sanity check, are the blinking rates equal if you replace the bulb that's burnt out?

What does "not work" mean? Does the fuel gauge indicate LESS fuel than actually exists, or MORE, or something else? Assuming you meant that the gauge just goes to "E" when you switch to the "bad" tank, it's likely either a bad sending unit in that tank, sunk float, or ground out at the crossmember. The fact that the other tank works proves out everything upstream of the selector switch (including the gauge itself).

What does "cleaned up" mean? Did you change things?

 

You have two wires wired backwards... I did this on the front when i replaced the socket and got the same fault..