Fuses blow for a reason – fix it right the first time or pay dearly later

While driving the car down the road, the car suddenly stopped running and a large amount of smoke billowed out from under the dash a sure sign of wires getting so hot that the protective coating was melting.

The repair on the vehicle identified what had actually caused the melt-down.  It was obvious that one or more wires were overheated either by an external heat source or from within. Since there was no evidence of a fire, it was decided that it must have been the wires themselves overheating. One characteristic of electricity is that the more current, or amperage, that runs through a wire, the hotter it gets.  Every wire is designed to carry a maximum amount of current.  The larger the wire, the more current that can safely be carried.  Similar to a hose carrying water, a fire hose can easily handle more water than a garden hose. The melted wire can best be appreciated by picturing what would happen to the poor garden hose if connected to a fire hydrant.

The next part of the puzzle was to determine why too much current had gone through the wires. Every vehicle is equipped with a fuse panel and the sole purpose of the fuses in the panel is to limit and protect the delicate electrical components from excessive current. It works like this when trying to protect the radio, computer and other sensitive electronics, the engineers protect them by putting in a weak link a fuse that is designed to burn out before any damage is done to the radio, etc. A fuse is equivalent to a one-time circuit breaker when too many things are plugged into one outlet, too much current tries to go through the wires. The circuit breaker turns off the power before the wires can be damaged. A fuse works the same manner it burns out and thus prevents the power from damaging the rest of your car.

In reviewing the fuse panel first. It was immediately obvious what had happened. As suspected, there was a 25 amp fuse in slot rated for 5 amps!  Some one had placed the wrong fuse in the wrong spot and exposed a circuit designed for a maximum of 5 amps to a maximum of 25.  Needless to say, this was trouble waiting to happen and it didn't let us down.

After identifying the reason for the burned out wires, the reason the fuse had been swapped still needed to be identified.  The wire diagram indicated that the burned out circuit powered, among other things, the passenger and driver side power mirrors. Inspection revealed that the passenger side mirror had previously been damaged and not properly repaired. While the proper repair was to replace the mirror it had instead been glued back together a sure way to cover up any excessive damage done inside to the wires that activate the motors that adjust the mirror.  No doubt it is this internal damage that caused the 5 amp fuse to continuously blow another tell-tale sign that an electrical problem exists and should be repaired, not swept under the rug and was improperly "fixed" with a 25 amp fuse that could handle the current.

The damage done to the Mesa AZ auto electric system was extensive.  The main wire harness (a harness is a collection of wires bundled together) that runs from the engine, through the inside of the car all the way back to the tailgate was damaged beyond repair.  In addition, another harness that runs under the dashboard was also damaged. In addition, the harnesses were a special order which put the owner out of their vehicle for nearly two weeks.