Contenu
Fuses are current overload protection devices, specifically engineered to act as the weak link in an electrical circuit. A fuse keeps a circuit from passing excess current and destroying whatevers attached to it or melting the wires and starting a fire. Automotive ignition fuse malfunctions pose a few unique problems, primarily since theyre usually not the only thing on that circuit.
Fuse Basics
Fuses come in all types and varieties, but they all work in a similar fashion. Current passes through the fuse via a small metal strip or a spring; that small metal strip creates a sort of bottleneck in the system, a point of high impedance where electricity will slow down and turn into heat. Once that strip gets hot enough, it melts, snaps and breaks the circuit connection. So, to find the source of your problem, youll need to look for an electrical short circuit that pulls more energy through the system than it was designed to handle.
Multiple Circuits
The problem with automotive electrical troubleshooting is that multiple systems often run through the same circuit or fuse. For instance, your ignition system might share its power source with the starter, fuel pump, fuel injectors, ignition control computer or that flashing skull shifter knob you bought from Pep Boys. So, the malfunction might not even be in your ignition system; it could be a malfunction or short circuit in any of the connected systems.
Ignition System Faults
The good news is that there arent too many things in the ignition system itself that can blow your fuse, particularly if the the ignition coil draws its current directly from the battery or alternator via a relay. If thats the case, then your fault is almost certainly in the ignition switch itself or the wires going to it. Within the distributor itself, a bad or bypassed ballast resistor can repeatedly blow fuses, but thats unlikely unless some hack mechanic did a bad wiring job on it. A bad coil might blow fuses, but itll more than likely kill the engine before that happens.
Ancilliary Faults
If your ignition system shares a common circuit with something motorized -- a fuel pump, cooling fans, power window motor, starter, etc. -- then thats likely the source of your fault. Electric motors always draw a certain amount of wattage, or amperage multiplied by voltage. Higher voltage makes the motor spin faster, more amperage causes it to produce more torque. If the motor seizes up or something forces it to slow down, voltage draw will drop and amperage draw will increase to maintain the same wattage. This can easily blow a fuse, particularly if its already heavily loaded by something as power-hungry as the ignition system.
Wiring and Computer Faults
Inspect your wires carefully; hot parts on the engine can easily burn through the wirings insulation and short the wires, and metal edges will cut through the wires and short them out. If youve got fuel injection, then you might be experiencing an internal short in the computer itself. In that case, youre out of luck; its off to the parts store or junkyard for a new computer.
