Hey, I have not done much diagnostics yet, but figured I would pick your brains before I start... I just recently got this truck, 85 f150 lariat, running after it sat for 11 years and the previous owner was in the process of fixing it up. One of the things he had done was replace the wiring harness so I fear I have a lot of work to figure out everything he did or didn't do when changing them out. I don't know how much you guys will be able to help, but here goes...

The dome light never turns off even with the doors closed. The blinkers work for the most part. When you turn the lights on, the switch seems to work normally, dimming and everything, however when you turn the blinkers on with the headlights on, the left blinker just turns on solid and when you turn the right blinker on it works but all the back lighting in the car blinks with the blinker... I have the light switch out but don't know the procedure for testing it to see if there is an internal short in it. Does anyone know where I can get schematics for the switch? Also, is there something that would cause the dome light to stay on other than the door switches or headlight switch?... Do I have to hunt down the short or is there a 'short cut' I can take? Thanks for any help.

 

If you have a friend at ford ask him to print up your wire harness diagrams for your truck year with updates. If you have no other choice get a service manual from a parts store. It should help you follow the wiring and figure out most wiring problems. Start with basics first. Does it run. Does it crank, does any of the electrical things work right. you need to purchase a VOM and a Circuit tester from Lowes or Home Depot. They will help you with every step toward a good truck. Following wiring colors through a circuit drawing will help you identify the ones your looking for. Then you simply test them with the circuit tester. Remember, if you short with the starting battery hooked up you burn. A bad day ! When you select a circuit, if you draw it out yourself on a clean sheet of paper you can better visualize its purpose. Remember the drawing has nothing to do with the physical placement of the wires in the truck. They usually follow a loom and you only see the shorter ends. The color code is your biggest key to what the wire does. Red doesn't always mean always hot, sometimes it is balck but green usually is ground while blue is a sensor but there are mixtures like yellow and white, red and white, purple and white, just a ton of combinations. Usually there is a color code box that tells you what to look for in the wires. Some of the wires have numbers on them. Happy New Year !

 

I had multiple manuals from the previous owner and I already owned a multimeter and have done a decent amount of electrical work on my own, I was simply asking if there were known problems with these trucks pertaining to electrical issues... The problem with the dome light was that someone had put a screw in it that didn't belong and was shorting it to ground. The problem with the blinkers was a ground not connected to the body and a short on the drivers side blinker. So we are out with the old on that issue... Thanks for your advice though.

 

If you can think of a problem, you may experience it. There is no sure fire electrical answers, only problems to be diagnosed.

 

Just learned so much, thank you! And I'm glad you got your lights straightened out bud, I got this impression of a light up Christmas tree making a left at a light lol or a very small firetruck maybe