1991 f-150 5-speed on the floor, 4.9L I6

Hey all... a few weeks ago, I noticed my turn signals and hazards were out, and switched the flasher. Nada. Pulled both 15 amp fuses at the 1 and 5 position and found them to both have been popped (also realized at this point that my backups and stop lights are also affected, hadn't occured to me before). So, I switched out the fuses, all was well. 45 minutes into my work commute, sitting at an intersection waiting to make a right-hand turn, I realize the idiot needle on my battery guage was wobbling like a sailor on shore leave... normally it pings a little when the turn signal is flashing, but this was extreme. Then, it stopped moving altogether, and it appeared my signal lights were again out. Pulled into the parking lot at work, found both fuses out AGAIN... luckily I had extras... I didn't even make it home from work before they were once again popped. I did some research, found out about this thing called a Multifunction Switch, except it wasn't called a Multifunction Switch for my model year... spent a few hours this weekend pulling the steering wheel and replacing the switch, wasn't as bad a job as I'd feared it would be... replaced previously bad fuses, tested everything, found it to work, there was much rejoicing... Didn't move the truck again until today, went to run an errand, used my turn signals maybe three times before the crazy needle wobbling began again and poof! the fuses are gone. Again. No brake lights, no backup lights, no turn signals, no hazards.

I could cry. I know it's girlie of me, I just might anyway.

The truck has just about 128,000 miles on it, and has been pretty low maintainence for it's age, which I attribute to the fairly low miles for a 17 year old truck. I'm pretty handy with repairs, but wiring remains a mystery to me. I am hoping someone has a simple explanation... or, at least one that makes sense. Any help appreciated....

 

99% of the time, the problem is at the rear bumper area with the wiring. This is where people cut the wiring and modify it for trailer hook-ups. Sometimes they get sloppy, and or the weather gets into the splices, and you run into trouble. Also when they go to sell the truck, they want the plug so they just cut the wires and leave them hanging. I would check this area out.

 

It's funny you should mention the rear end... this morning I replaced the two blown fuses again, figuring the problem to be with the flashers somehow and not wanting to be without brake lights, I would forgo using the signals at all and rely on the ole fashioned hand signals (thank God for warmer weather here in Phoenix...). I tested the brake lights a few times by tapping the pedal and looking in my side-view mirror... heard the tiniest of clicks, and gone again are the brake lights and hazards (same fuse, no idea why). Still had turn signals, however, then I noticed that the needle on the voltmeter pegs normally when I used the left-turn signal, and the crazy wobbling came when the right-turn signal was flashing... and then died. So... something in the back, right corner of my truck?

I had to replace lights and the wiring harness for my bumper-mount licence plate lights about two months ago - the new lights had one wire, the old ones had two, and I was told the new lights were self-grounding, so I didn't need to worry about not having a ground wire - when I crawled under the truck to do the replacement, the so-called ground wire on the old lights was just tied off around the frame, no metal to metal connection (I'm admitting my ignorance here). I do think everything is bundled, one big wiring harness for everything, including the tow lights and licence plate lights...

So... I replaced the turn signal switch for nothing? Oh well, at least I learned something, eh? Thank you for your help, by the way.

 

I've got an 84 F-150 and the tail lights won't work. I replaced the bulbs this morning and got the hazards and (I believe) the brake lights working. The tail lights don't come on though. I looked behind the bumper and sure enough, there were four wires hanging directly behind the trailer hook up. The truck has trailer brakes installed inside the cab. I am thinking these hanging wires are the problem, but I don't know what to do with them. Any help out there? Thank you.
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Do your license plate lights work? The taillights and the license plate lights are all fed by a brown wire. You can get a testlight or voltmeter and see which wire is hot with the parking lights on. It should be a brown. Then you need to find the brown wires from the taillights, and hook them all together.

 

I'll see about getting a voltometer and checking it out. So essentially the license plate light should be on when the tail lights are on then, right? Thank you! I'll let you know if I find anything new.

 

I have a 98 F150 2x4 with a 4.6. Several weeks ago i noticed I had no running lights in the rear. I had turn signals and brake lights. I just didn't drive at night for a couple of weeks or drove with my 4-ways on. Yesterday we got above 5c so started looking for the problem.
I traced the wiring harness back from the big connector above the drivers rear wheel. I had power coming to that plug but no power at the running light, and found a smaller plug with 5 wires running trough it. Pulled it a part and found the electrical pin in the plug for the brown wire corroded off, nothing left and when I was pulling the plug apart the yellow wire for the passenger rear brake light pin broke off from corrosion. Put a jumper on both wires and have running lights and brake lights.
Will check out junk yards for a slightly used wiring harness.