What Makes Car Fuses Blow?

The fuses installed in a car perform the same type of function as fuses installed in some homes and most electrical and electronic devices. When the current flowing through the fuse exceeds the fuse's current rating, the element in the fuse melts and breaks the circuit to discontinue current flow. When this happens, it means that whatever the accessory -- radio, wipers, horn -- the fuse is inline without allowing too much current to flow. The cause of this excess current should be immediately identified and corrected.

Faulty wiring or defective wiper motors can cause excessive current flow, resulting in a blown fuse. Defective switches may cause short circuits. Wipers frozen under ice can cause a blown fuse by impeding wiper movement. Other electrical components, such as heating and cooling blower motors, power seats, electric fuel pumps or air conditioner can all cause fuses to blow. In many cases a blown motor circuit fuse may indicate a shorted motor.

When troubleshooting leads to the confirmation of a blown fuse, the first thing to do is replace the fuse, making sure to exactly match amp rating. If this corrects the situation it may be the result of an intermittent power surge possibly caused by a bare wire, which should be located and repaired. If the failure is still present, do a thorough check of the wiring for loose connections in the failing circuit. Pay attention also to the battery lead attached to the motor and ensure a secure connection.

Replacing a blown car fuse is a fairly simple procedure. Most cars have small plastic-encased fuses that push straight in and pull straight out. Use needle-nosed pliers or small tweezers-like grippers made for this task. Replace the blown fuse with one of identical amp rating. Plastic fuses are color-coded so the replacement should be the same color. Glass fuse amp ratings are distinguished by differences in the length of the fuse. They are removed by lifting one end at a time. Discard blown fuses and obtain a new spare.

Some readers may have seen a "60 Minutes" program from a generation ago where a car was rigged with a simple malfunction and taken to several repair locations. Estimates for the repair varied over an incredible range for something that was just a few dollars to repair. Instances like this still happen each day. So it would be most prudent to check and replace fuses yourself before taking your car in for repairs. Car fuses are very inexpensive.