Blowing stoplight fuse only when car is started....

[dsm5062]

I am having a strange issue with my GVR4, it keeps blowing only the stoplight fuse in the under dash fuse box. I have already moved the side carpet and traced the loom it appears fine, changed all my bulbs and the stoplight switch, I even unplugged the taillights so it was just the harness and it popped the fuse. The strangest part is that if the car is just sitting for awhile after it has been running I can put in a fuse and the stoplights will work consistently even with the headlights on and key on but as soon as I start the car it will pop the fuse soon as I touch the brake pedal... and it will still pop the fuse for a few minutes after I turn the car off almost like its something holding some residual power for a short amount of time thats popping the fuse. Does anyone have any experience with something like this or have any idea what would cause this? the only thing I have left to do is slit open the harness and trace it from end to end

 

[dsm5062]

Well my problem just got stranger... I used a 194 socket with spade terminals in place of the fuse so the bulb would light when the short would occur. I unplugged all of the lights in the rear to eliminate the possibility of it being a socket or bulb and the short occured still so I crawled under the dash and noticed that the short wasn't happening when the stoplight switch was disengaged it was happening slightly further in the pedal travel almost like there is a wire shorting some where or something but I dont see any wires near the pedal or any surrounding wires that look like they are in the way of the pedal travel.

 

[dsm5062]

Well finally found the problem, the pressure switch for the ABS module was shorted out so everytime it saw a certain amount of pressure on the pedal it would short and blow the stoplight fuse.

 

[gofer]

Good find. I bet you feel a bit relieved after all that troubleshooting and wire chasing.

 

[dsm5062]

Absolutely!! it was definitely a challenge figuring this one out