Fuse instantly blowing????

[K85 Octane]

What causes a fuse to instantly blow when you press a switch? This has to do with my rear window on the K5. All was good until one day, pop. Dash and key are dead. Window works fine using jumper cables and a battery, but using either switch blows the fuse.

I've done a thousand things to the truck since the window last worked. Narrowing down what I did that *&<^#?*@$&*(%# the window is gunna be kinda hard.

 

[4X4HIGH]

There is a dead short to cause the fuse to blow immediately. I would check for any pinched wires along the frame rail on the drivers side first thing.

 

[Fordum]

Well, I hate to say this, but its caused by a dead short.........

In this case, it sounds like a cut wire or shorted switch.

You say the window works with a jumper cable and battery, but are the regular wires still hooked up when you do that?

If so, then the wire must be cut, otherwise you would get sparks and smoke when you hook up the jumpers.

If the wires are not hooked up, then you are going to have to make up a powered test light.

If you put power to the motor wires through a light, with the other battery wire hooked to ground, the light will light if the wire is shorted.
If so, then you just need to move wires and connections until you find the short.

Also, you can replace the fuse with a light bulb on wires. Then when you press the switch, instead of the fuse blowing, the light will light.

Tape the switch down, and start tracing and moving wires until the light goes out. Do that with the motor unplugged to eliminate a false positive.

Trust me, you have the best kind of problem. A hard short to ground that stays shorted is nice.

Its the ones that only short out every couple of weeks that take literally 5 years to find, like my old Jeep turn signals.

 

[Deuling]

Had the same thing happen when i took my gas tank out and put it back in. Where the straps bolt up there was a wire that ran right on that crossmember between the frames. put the nut on and forgot to pull the wire back. Hopped in, fired it up to test the new gas line and sending unit and turned the lights on. Heard a click and my dash lights went out.... Realizing the only thing i had done last was the gas tank i looked back there and sure enough i had pinched the wire. New fuse and off to the dunes i went

 

[rdn2blazer]

Don't forget to use rubber grommets through sheet metal where wires pass through. Rattling will wear the sheathing to bare wire quick.

 

[K85 Octane]

Is it possible I have a bad ground or would that just not make it work? Also, the jumper cables thing was to the wires coming out of the tailgate, so I know all tailgate stuff is good. I guess I'll start by disconnecting the main harness at the firewall and checking the dash switch, if I don't blow the fuse, I guess it's in the frame rail wires.

 

[dyeager535]

Not a bad ground. Leave the fuse out, use a multimeter set to continuity. Operate the switch while checking for continuity to ground through that fuse terminal.

Unlikely to happen, but I might suggest doing your testing with the battery disconnected. If you manage to blow a fusible link, you've made even more work for yourself.

 

[smier]

Definitely a short and not a bad ground. If it were a bad ground it just wouldn't work. Think of a tail light, if you were to disconnect the ground wire, it just doesn't light up. It doesn't blow the fuse.

 

[K5dreamer]

do any "unrelated" work on the truck lately? install stereo equipment? run mounting screws into any sheet metal? etc. etc.

ive seen it a million times, someone runs a screw into sheetmetal with "nothing" behind it, and the screw drills into a power wire, shorting it to the body.

 

[K85 Octane]

do any "unrelated" work on the truck lately? install stereo equipment? run mounting screws into any sheet metal? etc. etc.

ive seen it a million times, someone runs a screw into sheetmetal with "nothing" behind it, and the screw drills into a power wire, shorting it to the body.

That's just it bud, I've done 23,816 things to it since the window worked

 

[AKbigsub]

Also check the harness where it goes from the body to the tailgate. Quite common problem.