Goodness, gracious, great balls of fire! (Part II)

Auto parts

Last time we shared the eye-opening experience a customer of ours had while witnessing a vehicle fire. He was kind enough to take time to thank us for fixing the dangerous wiring system in his car to ensure he and his family are safe while traveling. So just what could have caused that car to go up in flames?

Faulty wiring can cause a fire. When any combustible material gets hot enough, it will burn. This can happen to a car that typically has some type of aftermarket add-on electrical device which has been improperly wired. When an automotive engineer designs a circuit, the circuit must be protected from damage with a fuse. A fuse is simply a small piece of wire designed to melt when a given amount of excessive amperage goes through it, thus stopping the flow of electricity.

A wire (or any conductor) is made up of many, many atoms. An electric current (electricity) is a literal flow of electrons from atom to atom. It starts at one side of the battery and is constantly trying to find its way back to the other side of the battery. It always follows the path of least resistance.

A simple formula for electricity is Ohms law, which says voltage equals amps times resistance. In a car, the voltage is mostly constant throughout the car at 12 volts. So if the resistance goes down, the amperage goes up and vice versa. It is the amperage that turns into heat.

Think of a headlight. The heat you feel with your hand is a product of the resistance in the form of amperage. The less the resistance, the more the amperage and heat. Your high beams are brighter and hotter. They use more amperage because they have less resistance in the bulb.

Think of a guy using an arc welder. As long as he holds the welding rod away from the metal, nothing happens because there is lots of resistance. But when he touches the welding rod to the metal, sparks fly. This is amperage at its best.

If your engine will not start and you have to keep cranking and cranking, the starter will heat up because of all the amperage it’s using. If you install a big stereo amplifier (or boom box), then your alternator has to work harder and heats up, supplying all the extra amperage.

Let’s go back to the fuses. Say someone installs an electrical device like an alarm, stereo, remote start or fog lights in your car, and does not wire it through a properly-sized fuse. If the device shorts to ground and has no fuse to blow, then the amps will increase in the wire until the wire begins to melt. It will melt everything it is touching. It will keep melting until there is no more resistance. This is how a fire begins.

We have seen vehicles with an intermittent short to ground in a circuit that keeps popping a fuse where someone has installed a higher amp rated fuse, rather than trace down the short. This is a recipe for disaster. We have discovered paper clips and tinfoil in place of a fuse, just to find melted and charred wiring downstream (as shown in the photo).

Whenever you add additional loads to your vehicle’s electrical system, remember to have a professional ensure the circuit is properly protected with a fuse. And it is not a bad idea to carry a fire extinguisher as an extra safety measure.


Wiring Issues