Headlights

When you are paying a mechanic by the hour, they do not have time to waste figuring out which fuse to check. It is much faster to grab a test light, and test each fuse. The spade-type fuses have two tiny holes on top for test points. Turn the circuit on, then check for voltage on both test points on every fuse. If you find 12 volts on both sides, that fuse is okay. If you find 0 volts on both sides, that circuit is turned off. You are looking for a fuse that has 12 volts on one side and 0 volts on the other side. That one is blown. You can test all the fuses in one fuse box that way in less than a minute. To add to the confusion, especially on newer vehicles, there can be multiple fuses for one dead circuit, and they are not labelled with easy-to-understand designations.

Be aware that safety systems like head lights usually are protected with auto-resetting thermal circuit breakers, not fuses.