Why does the fuse blow as soon as I start the car?

[MaverickRose]

The most likely reason for the ignition switch fuse to blow repeatedly is a short circuit or grounding issue in the related wiring. Here are the relevant details: 1. Fuse: A fuse, also known as a current fuse, is defined by the IEC127 standard as a "fuse-link." Its primary function is to provide overload protection. When a fuse is correctly installed in a circuit, it will melt and cut off the current when the current rises abnormally to a certain level and temperature, thereby ensuring the safe operation of the circuit. 2. Function: When a circuit malfunctions or behaves abnormally, the current may continuously rise, potentially damaging critical components in the circuit, burning out the circuit, or even causing a fire. If a fuse is properly installed in the circuit, it will melt and cut off the current when the current rises abnormally to a certain level and temperature, thus protecting the circuit and ensuring its safe operation.

[DiGabriela]

I've encountered the issue of burning fuses upon ignition several times. Initially, I thought it was due to poor-quality fuses, but later discovered it's often caused by short circuits in the wiring. It could be that the insulation on the starter motor's wiring harness is damaged, causing the positive and negative terminals to touch and create an overcurrent. Alternatively, the generator's voltage regulator might be faulty, causing the output voltage to exceed 14V. I remember one time when I tried to fix it myself—I turned off all the loads, replaced the fuse, and tried starting the engine, only for the fuse to blow again. This indicates the problem lies in the main circuit. It's best to use a multimeter to check the voltage and current, and avoid randomly replacing the fuse with one of a higher amperage, as that could be more dangerous. I recommend taking it directly to a professional shop to inspect the entire starting system to prevent damage to the battery as well.

[OBrady]

As a mechanic with years of experience, I can tell you that repeatedly blowing fuses usually indicates a ground short in the starting circuit. Possible causes include: shorted starter motor windings causing sudden current surges; exposed copper wires from aged wiring harnesses or engine vibrations making contact with the chassis; or even corroded fuse boxes. First identify which circuit the blown fuse serves - if it's starter-specific, focus on the motor assembly. Manually inspect wiring connections for looseness or burn marks. Don't just replace the fuse - test alternator output (normal voltage should be 13.8-14.4V). My professional advice: don't delay proper diagnosis to avoid complete electrical failure.

[DelGage]

If my car blows a fuse as soon as I start it, I would panic because this is a major hazard. It could be due to mice chewing through the insulation on the wiring or corrosion from a previous flood causing a short circuit. I remember my neighbor's car caught fire because of this. I would immediately turn off the engine and avoid using hazard lights to prevent adding more load. The key is not to underestimate it—a blown fuse indicates uncontrolled current flow, which could damage other components. First, check if the battery negative terminal is properly connected and inspect the wiring harness for any damage or discoloration. Safe driving is the top priority; don't skimp on towing fees and seek professional repair.