Automotive fuse boxes typically fail due to overheating. There are several causes for overheating, including added aftermarket electrical accessories or undersized wires or connections that were installed by the manufacturer, which sometimes result in factory recalls for the installation of new wiring harnesses and fuse boxes. If you have problems with your electrical system, you can check to see if your vehicle's fuse box is bad. Keep in mind that you should always use caution when working with an automobile's electrical system.
Raise the bonnet and remove the battery cable from the negative terminal. Inspect the fuse box, or power centre, located under the bonnet, often very near the battery. It has a black plastic lid and houses all the main power breakers. Remove the cover and inspect the fuses, circuit breakers and relays. Use a wrench to remove the hold-down bolts that attach the power centre to the car. It may also be necessary to remove the power feed wire from the battery to the power centre.
Lift the power centre and look underneath for heat marks, or a dark, blue halo discolouration. This is a sure sign that something is wrong with the box and a connection has failed. Remove the screws that hold the bottom cover in place. Inspect the connections. If there is damage, replace the power centre. Although minor repairs can be made, it is best to replace the entire centre.
Use a flashlight to inspect the inside fuse panel. Some car manufacturers, such as Honda and Mazda, use two inside fuse panels, one under each side of the dashboard. Remove the access covers and examine the fuses as well as the wiring going into the fuse panel. Dark, discoloured and burnt wires are signs of failure. Wires that have bubbles in the insulation have overheated. The panel and wiring will need to be replaced.