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Blown Outside Rearview Mirror Fuse
Posted to Technical Tips Forum on 12/16/2008 20 Replies


Truck I had about a month ago, fix might help somebody. This was a new-style Sierra 2WD. Complaint was "power mirrors inop". This truck had base power mirrors, no memory, just the fuse, switch and mirror motors. Schematic is SI doc ID 1848963 Customer had replaced the fuse twice, it now had a 5A fuse and it was blown. Spec is a 2A fuse in the left IP fusebox.

I started by installing a testbulb in place of the fuse and driving the vehicle and operating the mirrors, a short would hopefully light the bulb. No luck. Checked for TSBs and found 08-08-45-002 that talks about 2 concerns. First is harness damage caused by a trimpanel screw, second is possible loose or unplugged connectors at the mirror motors. I bit on the first possibility, and pulled both front doortrims to inspect harnesses. No luck. Then I used my Vantage Pro to current ramp both motors and saw 55-60ma running and 100-105ma with motor stalled, pattern always looked good. So I called Technical Assistance, looking for a silver bullet :) This gentleman was not much help, he thought I should pull both mirror motors and check for loose connections and then replace both motors for possibly being shorted. I explained that I had checked motor draw and it was never more than 105ma and it had blown a 5A fuse, he argued that a motor draws more current with high resistance or a bad ground, yada yada. I wasn't convinced.

Finally started thinking, decided to inspect the harness where it leaves the fusebox. Had to pull a couple trim pieces and then found the harness cut near the parking brake. Part of the self-adjuster is visible in the picture, a sharp lever that moves with the park brake. Several wires were damaged, almost anything in the Left door could be affected by this.

door harness at left passthrough

Talked to customer, he is an elevator repairman and we had a nice conversation. Last 10 years have brought major changes to elevator technology. I was surprised at what they can do now.

Robert from Florida

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car Vehicle Data

2007 GMC Sierra 1500 SLE 5.3L

Engine5.3 L
Trans4-speed Automatic (Electronic)