When we do this, we don't have time, (meaning your money), to waste trying to figure out which one or two of the dozens of fuses need to be checked. Also, a lot of circuits aren't even labeled for what you'd expect because a fuse can be protecting two or three unrelated circuits.
Most of the fuses are of the spade-type, and those have a pair of small holes on top for testing. You need a test light, but a digital voltmeter will work too. Poke the probe into those two holes, one at a time. You'll need to turn the switch on for the circuit that doesn't work, in this case the head lights. If you find voltage on both test points for a fuse, that one is good. If you find 0 volts on both test points, that circuit is turned off. The fuse could be blown, but it would affect some other circuit. You're looking for a fuse that has 12 volts on one test point and 0 volts on the other.
By testing this way, we can test two dozen fuses in less than a minute. It doesn't matter how they're labeled; if we find one that's blown, we just replace it. If it blows again, then we have to diagnose the problem further, but quite often they blow when simply connecting the battery, or in your case, by causing a momentary short when working in the circuit when it's turned on.
There are larger cartridge-type fuses too but those protect multiple circuits that are each protected by the smaller fuses. It's rare for a cartridge fuse to blow. Those can usually be inspected visually through their clear tops.
Tuesday, July 14th, 2015 AT 5:07 PM