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A short shortcut
Posted to Technical Tips Forum on 3/8/2014 54 Replies

Maybe a tip like this has been posted before, if it has I apologize.

This week I had a car that was blowing 6 fuses. One of them instantly and the others would blow randomly. I had suspected a pinched harness somewhere. I decided to follow the circuit that blew the fuse instantly.

That would be the 40 amp power window fuse. It was a dedicated fuse for the 4 window motors and switches. The harness leaves the under dash fuse box on the left side and somehow goes to all 4 doors.

I installed my 30 amp fuse saver breaker into the receptacle for the window fuse. Now this circuit goes all through the car. In the past I would have cut wires if I could not disconnect a connector to find the general zone of the short.

This time I put my amp probe around the harness in the rh kick panel to see if the short was in the passenger side doors. Resetting the breaker and keeping an eye on the meter no current flow was observed. When I put the amp probe around the power window wire in the left kick panel and reset the breaker a brief 38 amp draw was observed before the breaker popped.

Now I know the short is between the under dash fuse block and the lf and or door. Putting the probe around both wires in the door breakout harness showed no current flow. Ok the short is in the harness between the fuse block and door breakouts. Followed the harness and found it went under the carpet on the drivers floor. Seeing as this would be the area that would get the most use I pulled up the carpet on the drivers floor.

Bingo there it is! The window wire had corroded which caused it to create heat and melt the harness causing all the other fuses to blow too.

So what I learned was instead of disconnecting harness to zone out a short , if you use an amp probe to see if there is current in that particular part of the harness you can narrow down the location of the short.

Robert from New York

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