How to Wire Accessories to Car Fuse Panels

While car batteries typically only produce 12 volts of current, they produce high amperage levels that could cause quite a jolt if you're not careful. Therefore, before you do anything else, open the hood and disconnect the negative (black) terminal from the battery. This precaution will ensure you do not shock yourself while installing the new wiring and prevent possible short damage to your fuse panel or accessory. Before disconnecting the battery terminal, switch off the ignition. You can then use a small crescent wrench to loosen the terminal bolt and remove the cable. If you have a wrench set, you'll probably need to use the 8mm or 10mm wrench to remove the bolt, depending on your vehicle.

Take a few minutes to gather all the tools you'll need to perform the task. The tools you need may vary slightly depending on your model vehicle, and the method you choose to wire the accessory to the fuse panel. Some older vehicles may have screw terminals you can use to wire new devices rather easily. However, many newer vehicles often use pin-blocks or solder terminals that make wiring to the fuse panel rather difficult. In such cases, you'll find it much easier to use a fuse tap. A fuse tap plugs into the panel like an actual fuse, but has a connector on the opposite end that allows you to create new circuits and wire new accessories or devices. In addition to the fuse tap, you'll need some electrical wire, a pair of wire crimpers, a Phillips screwdriver and possibly some Velcro-type hook-and-loop tape. If your objective is to wire an accessory with a cigarette lighter adapter cable to the fuse panel -- to free up the cigarette lighter in the vehicle for use with other devices -- you should probably purchase an add-on 12V power outlet as well. Clipping the wires on the cigarette lighter adapter cable will probably result in the device not working at all -- especially if the device is an AC device designed primarily for use in the home.

Wiring the accessory to the fuse panel is relatively simple. Nevertheless, it can be a bit tedious wiring the accessory to ensure a proper ground and that the wiring just doesn’t lay across your seats or floorboard. Depending on your vehicle, the fuse box is probably underneath the dash near the gas and brake pedals or inside the glove box. Whether you need to remove the dashboard to wire the accessory will usually depend on where you plan to use the device inside the vehicle. If you want to mount the accessory to the dash, you'll probably need to remove the center part of the dash or the console. If you want some slack in the wiring so you can use the accessory in either driver's or passenger-side seat, using some hook-and-loop tape to secure some of the wiring underneath the dashboard should suffice. Avoid running wiring underneath the floorboard carpet unless you will use protective sheathing, as it could be a potential fire hazard if the wires become damaged or frayed. In addition to the power wire that you must run to the fuse panel, you must also wire the ground for the accessory. Therefore, you'll need to find a grounding screw on the firewall of the floorboard behind the engine well. If you cannot find a grounding screw, you can use a self-tapping metal screw to create one. If you go this route, though, you'll need to seal the screw hole with silicone or another waterproof sealant.

If you are connecting a true automotive accessory, wiring the device is relatively straightforward. Just connect and crimp the power wire from the accessory to the fuse tap, plug the fuse tap into an open slot on the fuse panel, and then secure the ground wire from the accessory to a grounding screw. However, if you want to wire a phone, MP3 player or other device that usually uses an AC power adapter, you'll need to add a 12V power outlet to the circuit. Add-on outlets such as the Enercell 12V power accessory outlet connect easily to a fuse tap and allows you to use your AC powered devices with a cigarette lighter adapter cable (link in Resources). Because the power accessory and adapter cable for the accessory perform the conversion from AC to DC, you don’t need to worry about wiring the common or negative lead for the device. If you try to snip the cigarette adapter cable for the device and connect it to the fuse panel, you'll find you have no place to connect the negative wire. Most cigarette lighter adapter cables contain three wires: positive, negative and ground. Adding an 12V power outlet lets you get away with using only two: the positive and ground. After you connect the new power outlet to the fuse tap and panel, you can then simply plug your accessory in and use it normally.

If you opt to use a fuse tap, choose one that has slots for fuses rather than one that offers no short protection and only provide a straight-wire connection to the panel. Some fuse taps allow you to draw power from the panel without any fuse at all. Straight wiring the device without a fuse could result in a fire hazard as well as damage the accessory. Additionally, select the proper fuse size for your device. If installing an amplifier, car stereo or other automotive accessory, the user guide or manual should state the proper fuse size to use with the device. In most cases, using a 10-amp or 20-amp fuse should suffice for accessories. The fuse size dictates how much amperage can pass through the circuit before the fuse fails or "blows". Although a smaller amp value means the fuse will fail faster, it also protects your devices and accessories from potential damage. Therefore, use the smallest fuse size possible that enables you to use your accessory if the user guide or manual does not specify a value to use.