What You’ll Need Before You Begin
Depending on the complexity of the job, you’re likely to need:
Wire strippersSoldering iron or crimping toolDigital multimeter (or a test light in a pinch)Solder or butt connectorsProperly sized gauge wireElectrical tape or heat shrink
Check the Circuits
Use a wiring diagram (if you have one) to find the wires to connect your new equipment. Use a digital multimeter (DMM) to check that you have the right wires, check the circuit polarity, and verify the proper voltage. A test light will also do the trick in a pinch, but tests are a little different from DMMs. Because test lights use incandescent bulbs to indicate the presence of voltage, they put a load on the circuit. That’s not a big deal in most cases, but if you have a DMM, it’s better to be safe than sorry.
Disconnect the Battery
Always disconnect the car battery. Leaving the battery connected while you’re wiring in new electronics can damage the new device or other equipment in your car, so just pull the negative battery cable. The only times the battery should be connected are when you’re testing wires to verify that they have power or ground, and when you’re testing your new equipment before you button everything up. If your wiring project doesn’t involve replacing the factory radio, make sure that the existing head unit doesn’t have anti-theft protection that kicks in whenever the battery is disconnected. If it does, you’ll need a special code to get the radio working again. The code or reset procedure is sometimes in the manual, but the service department at your dealer can help if it isn’t.
Use a Wire Stripper
Always use a wire stripper to strip wires. If you use scissors, a razor blade, or another sharp object, you might accidentally cut all the way through the wire or generally make a mess of things. With a wire stripper, you can take off the proper amount of insulation every time.
Don’t Use Wire Nuts
Wire nuts are fine for the electrical wiring in your house, but you don’t speed down the freeway at 70 mph in your house or take it down bumpy back roads. The vibration a vehicle generates on the road can loosen even the tightest wire nuts over time. In a best-case scenario, that will simply cause your device to stop working. In a worst-case scenario, something might short out.
Use Solder or Butt Connectors
The best way to complete any DIY wiring project in your car is with a soldering iron and electrical-grade solder. A good solder joint will stand up to routine vibration and protect wires from oxidation. If you don’t know how to solder, butt connectors are another solid option. These connectors look like little plastic tubes with metal sleeves inside. Strip the wires you want to connect, slide the wires into the butt connector, and then squeeze it with a crimping tool. This is the easiest way to wire any new electronics, but you need a crimping tool to do it properly.
Insulate Your Wire Connections
The last, and possibly most important, DIY wiring tip is to insulate your connections. Whether you use solder or butt connectors, proper insulation will help ensure that your wiring job doesn’t fall apart, corrode, or short out in a few years. Heat shrink is the best way to insulate wiring connections, but you must remember to cut the tubing and slide it over the wires before connecting them. You can then slide it over the connection and heat it up until it creates a tight seal around the wires. Some soldering irons have special tips that are designed to activate heat shrink tubing, but simply placing the tip of a hot soldering iron near the tubing will often do the trick. Electrical tape works, too, but you must use a high-quality product. If you use low-quality electrical tape or the wrong kind, it can peel off, crack, or wither over time.
