How To Wire a Car Radio to a Fuse Box
By Jeff Grundy
If you are replacing the factory radio that shipped with your automobile, the car probably has a wiring harness you can tap into when installing a new stereo. The wiring harness for a pre-existing stereo usually negates the need to wire the new radio for power and ground. However, if you want to add a radio to a car without one, you may have to wire power and ground for the unit to the vehicle's fuse panel underneath the dash. Although installing new electrical wiring for the radio may seem complicated, it's relatively simple as long as you are comfortable using a few hand tools and know some basic wiring methods.
Don’t Get Shocked
The battery in your car may only produce 12 volts of power, but it delivers a lot of amperage. The high amps produced by a car battery can provide quite an electrical shock if you get careless while wiring your car stereo to the fuse box. Therefore, before you get started, pop the hood on your vehicle and disconnect the negative battery terminal cable -- the black one. This precaution will prevent you from being shocked while working with the wiring. Just to be sure, switch off the ignition and remove the key as well.
Choosing a Connection Method
If you're installing a new radio into an old vehicle -- say one made in the 1970s or earlier -- it may use the older tube-type fuses and its fuse panel probably has screw terminals you can use to hard wire new fuses and devices. However, if you are adding to a radio to a 1980s or newer model vehicle, it probably use the more familiar plastic, flat edge fuses. Adding new wiring directly to a modern fuse box can be tricky and usually requires some advanced soldering skills. However, you can save considerable time by purchasing a fuse tap. A fuse tap plugs into the fuse box just like a normal fuse and has a wire with a crimp connector you can use to connect to the power wire from the car radio. So, if you are installing a radio in a relatively new vehicle, using a fuse tap is definitely the easiest method.
Supplies and Tools
Once you have your fuse tap, the only tools you really need to connect the car radio to the fuse box are a wire crimper tool and a utility knife. If you are installing the radio in a classic vehicle, you'll need a Phillips screwdriver to connect the wire from the radio to the fuse box. Of course, you will also need a fuse rated with an amperage value rated for your car radio. You should be able to find the recommended amperage rating for the fuse in the radio installation guide. Most low-powered radios can use a 20-amp fuse without any issues. However, for high-powered stereos -- those that produce 100 watts of power or more -- you may have to use a 25- or 30-amp fuse. You may be able to use a wire clasp or harness already under the dash to secure the wiring from the radio to the fuse box. If there is no available clasp or harness, though, you can use some ordinary electrical tape to secure the new power wire for the radio to an existing wire bundles beneath the dashboard. The only other items you might need are a piece of 12-gauge electrical wire and a butt connector if the power wire from the radio is too short to reach the fuse box.
Running the Wire
Running the wire from the radio to the fuse box is relatively simple. Just use the crimp connector to attach the butt connector and 12-gauge wire length to the power wire on the radio and then secure the wiring to a harness or wire bundle. You shouldn’t have to remove the dashboard to run the wiring from the radio to the fuse box, but you may have to crawl under the steering wheel to do so. Additionally, if you have already inserted the car radio into the dash and secured it, you may have to remove it so you can access the power wire. Don’t forget that the radio also has a ground wire that you must secure to a metal part of the car chassis. There should be a grounding screw near the firewall of the engine compartment to which you can secure the ground wire. If there is not a ground screw or terminal available, you can can create your own by screwing a self-tapping metal screw into the floorboard or firewall instead. If you use a self-tapping screw, be sure to use some silicone or rubber epoxy to seal the screw hole to prevent damage to the vehicle due to moisture or rust. When you run the power wire to the fuse box, leave a couple of inches of slack for connecting the fuse tap.
Connecting to the Fuse Box
Once you run the wire from the radio to the fuse box area, you're almost done. Just strip away about half an inch from the end of the power wire, and then insert the bare wire into the butt connector on the fuse tap lead. Use the crimp connector to secure the power wire to the lead, and then plug the fuse tap into an available slot in the fuse panel. If performing the job in an older car, first strip about half an inch from the end of the power wire. Then use the Phillips screwdriver to secure the bare wire to an unused terminal on the fuse box. Insert an appropriately rated fuse into the slot on the head of the fuse tap plug -- or the fuse box itself in classic vehicles -- and you're done. Just reconnect the negative battery cable, turn on the ignition and fire up the radio. If you have already connected the radio to your car speakers, it should be able to play music immediately.
It’s not uncommon to see people wire radios to the fuse box by inserting the power wire directly into a fuse slot and then inserting a fuse on top of it. Although this may work, it is also dangerous and could damage your new radio or create a potential fire hazard. You should also avoid using a fuse with a higher amperage rating than that specified for your new radio or stereo. While the radio will still work, you defeat the purpose of the fuse by using one with a higher amp rating. A fuse amp rating indicates how much current, in amperes, the circuit can withstand before the fuse blows. If you use a fuse with too high a rating, it may not blow or fail in time to prevent damage to your radio. For instance, using a fuse rated at 25 amps with a 15-amp car radio may allow too much current to pass through the circuit and cause irreparable damage to the stereo.
Jeff Grundy has been writing computer-related articles and tutorials since 1995. Since that time, Grundy has written many guides to using various applications that are published on numerous how-to and tutorial sites. Born and raised in South Georgia, Grundy holds a Master of Science degree in mathematics from the Georgia Institute of Technology.