If you find a blown fuse in a circuit or piece of equipment pay attention to the fact this represents a symptom – it’s not the cause of the problem.
Blown fuses mean either a spike has been induced into the circuit or a circuit has reached overload because a higher wattage device or component has been connected. And if this occurs when you’re upgrading a circuit to carry a higher wattage, be sure you check the wire size before you start beefing up the fuse circuits. The last thing you want is a fire.
Blown fuses might also indicate an overload caused by a short in the circuit that is bypassing whatever load exists. When you’re searching for a short consider that damage to cable is most likely to occur wherever there’s highest resistance in the circuit. To find the short circuit, take off the load component of the circuit and test it looking for a zero or close to zero ohms reading across its terminals. If you get such a reading it means the short is in the load but if there’s a normal reading, the short is in the circuit itself.
Leave the load out of the circuit and replace it with your DMM with power and battery disconnected. With power disconnected you are looking for a reading of zero ohms – anything more indicates a short in the circuit. It’s not too hard to pinpoint a short in a circuit by exploiting a switch or break in circuit. If a break in the circuit has no impact on the meter reading, the short exists on the meter side. If the meter reading goes to O.L when the circuit is opened, the short is on the other side of the opening.
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