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On a long fuse!

What happens if you install a fuse with the wrong amp rating? This and some other tips by Ranojoy Mukerji will help you maintain the electrical components in your car.

india Updated: May 21, 2003 15:54 IST

Lights are one of the most critical components of a car. This in turn means that the electrical system has to be in top order for the lights to work and more often than not it is the wiring and the fuses, which are responsible. The fuse panel inside the vehicle is usually meant for headlights and electrical accessories such as the heater, radio, power windows, seats, defroster, etc. The one under the bonnet is for high amp systems such as the ignition circuit, fuel injectors, starter motor, fuel pump and antilock brake system (ABS).

The fuses under the hood are typically large capacity fuses (30 amps or more) while those inside a vehicle are typically 20 amps or less. A fuse is a protection device that is designed to blow if the amp load in a circuit exceeds the “safe” limit for that circuit. Fuses are built with a specific amp rating, which is marked on the fuse. The wiring and design load of the circuit dictates the size of fuse that is required to protect the circuit. Circuits that draw a lot of power need fuses with high amp ratings (20 or 30 amps) while those that use minimal power require smaller fuses (5 to 15 amps).

When the current in a circuit exceeds the normal limit, the metal element in the fuse melts and opens the circuit stopping the flow of current. A short, for example, causes a runaway electrical current. If not stopped, wires can start to melt and things can catch fire. So, respect the amp ratings specified for fuses (found in your vehicle owners manual, on the fuse block itself or a fuse block reference decal).

What happens if you install a fuse with the wrong amp rating? If you install a 20-amp fuse in a circuit designed for 10 amps, you are asking for trouble. A difference of 10 amps might not sound much, but it may be enough to fry a sensitive electronic component or to overheat wires to the point where the insulation may start to melt. Under no circumstances should you ever bypass or eliminate a fuse.

The fuse for the windshield wiper circuit may blow if debris builds up in the cowl areas and interferes with the movement of the wiper arms. If a fuse blows in a motor circuit (heater blower motor, cooling fan motor, power seat or window, electric fuel pump, etc.), it often indicates a shorted motor. If a fuse in a light circuit blows, look for wiring or connector shorts. Adding driving lights may also overtax the headlight circuit unless a separate circuit is provided for the driving lights. An A/C fuse will blow if the system is low on refrigerant and is working hard.

All these tips are essential to keep your car electricals working in good order and to ensure that your car lights keep burning for years to come!

First Published: May 21, 2003 12:41 IST