This is a universal guide for hooking any 12V device up to your car. Anything from LEDs to neons to an amp and subwoofer. This guide focuses on smaller gauge wiring than typically used in an amp but the concept is the same.
Instructions
1. First make sure your wiring is compatible. It should be heat resistant because it's going in the engine compartment. Most hardware stores sell wiring specifically made for cars in their car department. The most common type of wire to use is stranded copper. Make sure it is the correct gauge to carry the amount of current that your device pulls. You can calculate it if you know the watts. For instance, an inverter powering two 12" neons is usually about 40 watts. So divide 40 by 12v and you get 3.3 amps. Pretty much any gauge of wire can carry that much. For most purposes 16 or 18 gauge wire will be sufficient because it can usually carry at least 10 amps. Check the wire's ratings on the package to make sure. If you want to make things really easy on yourself later, get two spools/packages of wire, one red and one black
2. Make sure your fuse is rated for the correct amount of amps as calculated above for the wiring. Usually it's best to have the fuse be about 50% higher than the expected amount of amps. So for example and 8 amp device should have a 15 amp fuse. Check out the picture to see the best types of common car fuse containers and the fuses that go in them.
3. Now make sure your ring terminal connector fits onto the bolts that are holding the clamps onto your battery terminal. If you've never seen a ring terminal connector, check out the picture. These rings will go on the bolts beneath the nuts
4. Now you need to open your car's hood and locate the battery. It's the huge box shaped thing with two terminals and wires coming off of it. Make sure your car has been off long enough to cool off because it's easy to burn yourself while working in a hot engine compartment.
5. Now it's time to decide which way you're going to run the wires. There's 2 common choices. One is to go from the battery to the side of the engine compartment and through the space between the side mirror and windshield right by the hinge of the hood. This will have the wires come out at the top left corner of your dash behind the steering wheel. From there you can run the wires across the dash, down the side of the dash, or through the ceiling. The other path is from the battery to the side of the engine compartment then across the rear of it and straight down to the hole in the car's firewall (metal wall at the back of the compartment). There should be a rubber stopper there called a grommet. If you run the wires this way, all you need to do is cut a tiny slit in the rubber and run the wires through. This way the wires will come out around your gas and brake pedals. The wires are more hidden this way and you can easily run them under your center console or your dash with less wire.
6. If you were smart and bought two reels of differently colored wire, tape the end of each to the middle of the battery, NOT the terminals, to simulate the required distance as if they were actually connected. Then run the wires to the side of your engine compartment and up it to whatever path you chose. There should be unused holes drilled on the ledge there where you can use wire ties to hold the wires in place. If you don't know what a wire tie is, check out the picture for this step. It is very important that the wires be held tightly to the side so they don't move freely inside the engine compartment. Make sure you don't run the wires around or touching places that get hot like the radiator tubing and also avoid moving parts like belts. Then run the wires through your chosen path. Once you're sure you have the length correct so the wires will reach from your battery to where your 12V device is going to sit, cut the negative wire. If you had to run the wires twice because you only bought one spool of one color, put some masking tape around both ends of the negative one and cut it then run the positive wire. If you did color code them, black will be negative and red will be positive.
I should mention that since your car battery is grounded on the car's chasis, it is possible to skip running a negative wire and attach your device to the chasis with a much shorter wire. This is way more dangerous and you have to sand and drill a hole in your chasis and after doing that, you may find out that it's a very poor place to attach it and doesn't conduct well and you've got a hole in your car for nothing. So just run a seperate wire.
7. Now it's time to add the fuse to the positive wire. Pick a location that you would like your fuse holder to be. Beneath the dashboard, under the steering wheel is a popular place. Just remember wherever you put it, you're going to have to get back in there to change it if it ever blows out. Cut the positive wire so it's long enough to reach your chosen location and strip it. Strip both ends of the fuse holder's wire if they're not already and attach either end to the positive wire you just ran. I made a diagram on twist and seal two wires together and attached it to this step. It's a little fuzzy but you'll get the idea. Just twist the two together tightly, push the twisted bunch to the side, and wrap electrical tape around it tightly. Make sure you're using electrical tape that's safe up to 180 degrees Fahrenheit and if you live somewhere where it gets cold, safe to 0 degrees Fahrenheit too. I'd strongly recommend using 3M's Super 33+ vinyl electrical tape because it has those ratings. That stuff is super tough and never melts or flakes off. This is one of the only safe ways to safely join two wires in car applications. Those wire caps that are used in house wiring can fall off and cause a massive short and aren't water tight so DO NOT use them. Attach the end of the remaining wire to the other side of the fuse holder now and join it the same way.
8. Now you need to choose a location for your switch. I attached mine to the center console with VHB tape but you may want to stick it somewhere on your dash or another location. Some common rocker and toggle switches are shown in the attached picture. There are thousands of different types of switches so shop around and find one you like. Note how they have two plug-like terminals on them. Avoid buying ones with three because they won't be useful in this particular application. Also make sure they are rated for at least the amount of amps you're using. Most are rated safe up to 25 amps. If you need one that can handle more, you may need to use breaker or battery main line cut off switches.
9. Now that you've chosen a location for the switch, run the positive wire to the location and cut and strip it. Strip at least a full inch off the wire because you're going to need enough to run it through the hole in the plate on the bottom of the switch then back down and twist it around so it is secure. Twist it as tightly as possible then wrap the entire thing in elecrical tape. Cover as much metal as you can to prevent shorting. It won't actually "short" in the traditional sense since both lines are positive but it will turn your device on while the switch it off if it shorts and you don't want that. Connect the reel of positive wire to the other side and run it to where the negative wire ends. This way the switch effectively acts as an interrupter to the positive line. Make absolutely sure that the switch is turned OFF at this point.
I know someone will mention this if I don't so...there are socket attachments you can add to the ends of your wires like the ring terminal connectors that slip onto the switch's plugs but my way was faster and cheaper.
10. So now your positive line is fused and switched and is alongside your negative one. Now strip the wires and attach them to whatever device you're powering and mount it in place (if that's what you're doing with it)
11. Now all you need is power going to your device. Go back to your engine compartment and untape both wires from the battery. Strip both ends and attach ring terminals. To attach them just stick the stripped wire into the bottom of it and use a pliers or wire stripper with crimper to flatten the metal tube holding the wire. Be careful that the wire doesn't slip out because it probably won't be very secure even after crushing the metal tube. Wrap several pieces of electrical tape around the plastic casing and the wire so it won't slip out. Once each lead has a ring on it, unscrew the negative battery terminal's clamp. The negative one should have a thick black wire coming off it and the other should be red otherwise the terminals should be marked + and -. Note that the nut on the bolt that applies pressure to the clamp sometimes does not come completely off because the bolt's threads were purposely cut at the top. If this is the case, you can loosen it and use two pronged, forked connectors instead of full rings on the ends of your wires. That will allow you to slip them on without having to take the bolt/nut completely off. Otherwise try to use a different, removable bolt attached to the clamp. If your car's terminal clamps only have one bolt, you may want to consider replacing them with ones that have a separate offshoot with a bolt for this exact purpose. See the attached picture for an example of a terminal with a second bolt to attach a ring to. The thin, red wire is tightly held on with the ring between the washer and clamp body. Yours should closely resemble that. When you have the negative wire attached, do the same with the positive and make sure both are very tight.
12. Now that you have power available, add the fuse to the fuse holder. The direction doesn't matter but it may only fit one way. It is important that you don't add the fuse until this point to avoid getting electrocuted or burned by large sparks when connecting the rings to the battery. Now that the fuse is in, flip the switch to the on position and your device should receive power and turn on (if that's what it does when it first receives power). If anything other than that happens, turn the switch off immediately and check the fuse and all connections to make sure it's all correct. If everything appears to work correctly, leave your device on for at least 2 minutes with your car off to make sure no wires heat up and melt and there are no shorts. Most car fuses don't blow immediately if the current limit (aka the amp rating) is exceeded. If the fuse does blow, check for shorts in the wires. A short is when the metal parts of the negative and positive lines touch each other. If everything is all set, double check that your wiring isn't going to fly around in your engine compartment and close the hood and start your car. Make sure you open your garage door first to vent the exhaust if that's where you are. With your car off the voltage on that circuit should be around 12.5V but with it running it should be around 14.5V and may be as high as15.5V in extremely cold weather. Ensure that your device won't get damaged by that high of voltage by leaving it powered on while running the engine for at least 1 minute. If it is meant to go in a car, it's an engineering standard to have it be able to run at voltages between 10.4 and 14.7 so there shouldn't be a problem.
Tags: engine compartment, your device, positive wire, make sure, electrical tape, fuse holder