1999 Ford F150 XLT 4.2 V6
Left turn signal is blowing fuse with a catch!!!


Ok, So I keep blowing fuse 13 when I put on my turn signals. I then noticed only the left signal did it.
I have done the steering wheel wiring at the MFS. no change.. I replaced the MFS also no change. Replaced the Flasher relay, no change. removed the CC connection at the brake cylinder (recall service was performed a long time ago) still no change.
So each time I replaced something, I would check it in the drive way and it seemed to fix it. Then as soon as I went for a test drive, it would blow the fuse with the left turn signal.
After one of these frustrating drives, I replaced the Fuse and tested the turn signals... It worked...
So I get in, and decide I will leave the Left turn signal on go for a drive keeping it on and see what seems to happen to make it blow.
I didn't get far, as soon as I got in, I closed the door and Pop the fuse blew. replaced the fuse left the door open and tested it again and sure enough it works if I leave the door open. As soon as I close it, the fuse pops.
I removed the door panel. and I unplugged all of the wiring I could, but as soon as I closed the door is would pop again.
Any Ideas? What from the door is also part of that circuit? I have looked in the wiring diagrams, but cant seem to find anything.
I have not looked at the wiring that goes through the door to chassis to determine if something is shorted or not, but if the door is open and I grab and twist the rubber tube with the wires, the fuse does not blow.
Is there a connection between the door ajar sensor and fuse 13??? that is the only connection I cant remove in the door.
Any Ideas?

 

Your problem sounds to me like a dead short in your left turn signal wiring, in my 03 the harness that contains that wiring is along the driver side frame rail. I wouldn't suspect the wires there are at fault. But if you pop out the left tail light you may find a pinched wire in that area. Likewise if you don't discover a frayed wire at the rear, check up front. I suspect by shutting the door you rock the truck enough to move the wire and pop.
let me know if you find something!

 

Thank you for the comment...I have checked all the wires for dead short. Removed all of the lamps in the turn signals and it still blows when I close the door. Even if I do it really lightly.
If it is only because I close the door...and you are suggesting that something shifts in the body somewhere... One would think that every once in a while it would either blow the fuse with the door open or Not blow it when the door is closed. BUT in this case, if the door is open it works, and if the door is closed, it blows the fuse EVERY TIME. I will be opening the rubber tube and looking at the wires where they go through the door to the body. But again, I cant find anywhere that the door wiring connects with the turn signals... Unless something is sending power to a ground wire when I close the door.
I am also wondering if the Door Ajar circuit has something to do with it. Like when I close the door, the Latch that tells the circuit to turn off the dome light and door ajar instrument cluster lamp to turn off causes an issue...

 

You have turn signal mirrors? Or maybe pre-wired for them?

I'd look at the harness in the door hinge area, or inside the door itself, sounds like you are narrowing down the area based on your symptoms

You're looking for a direct short of a power wire to ground to cause a blown fuse. (It's probably blowing the fuse wide open)

 

Patman, I'm pretty sure ford didn't put repeaters in the mirrors in 99. As I stated above I'd be willing to bet it's a pinched wire either in the front, or much more likely it's at the rear tail light. I've had my 03 apart a few times and there's all kinds of sharp edges that a wire could fray on. Shutting a door could easily shift it enough to cause it to pop the fuse

 

I just pulled diagram for 1999 and assure you side mirror repeater were equipped.

Left side is LG/WH (light green with white stripe)

 

Any updates?

 

Yes...I have it fixed. Not sure what color wire it was but there were 2 wires wrapped in black tape along with others in the plastic tube at the drivers door that were broken/bare, and I assume touching.
That said, I have no idea what they went to, because all my stuff works on the door...
I could not tell the color because the black tape was so friggin messy. I put tape on them and tested everything out. It seems to be good now.

 

Good find. Glad you got it figured out!