DIY Car Wiring Tips

Avoid shortages and malfunctions when wiring your car's electronics

Before you start any DIY wiring project, it’s vital that you have the right know-how, as well as the right tools and materials for the job. Whether you're installing a head unit or replacing a headlight, there are a few basic tools you will probably need, depending on the complexity of the job:

  • Wire strippers.
  • Soldering iron or crimping tool.
  • Digital multimeter (or a test light if you're in a pinch).

In addition to your tools, you will need some materials to complete a DIY wiring project:

  • Solder or butt connectors.
  • Proper gauge wire.
  • Electrical tape or heat shrink.

Check the Circuits

Fluke DMM being unboxed
Fluke DMM. Hiroshi Ishii / Flickr / Creative Commons 2.0

If you have a wiring diagram, you can use it to help find the wires you need to connect your new equipment. It’s still a good idea to use a digital multimeter (DMM) to check that you have the right wires. With a DMM, you can check the circuit polarity and verify the proper voltage.

A test light will also do the trick in a pinch, but test​s are a little different from digital multimeters. Since 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

Disconnecting the battery of a car
Dave Schott / Flickr / Creative Commons 2.0

One of the most vital tips for any DIY wiring project is to disconnect the car battery before you get started. The only time the battery should be connected is when you’re testing wires to verify that they have power or ground, or when you’re testing your new equipment before you button everything up. Leaving the battery connected while you’re wiring in new electronics can result in damage to either the new device or other equipment in your car, so it’s a good idea to just pull the negative battery cable.

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 to know a special code to get the radio working again. The code or reset procedure is sometimes located in the manual, but the service department at your local dealer may be able to help if it isn't.

Use a Wire Stripper

Self-adjusting wire stripper on tile floor
Self-adjusting wire stripper. Andrew Fogg / Flickr / Creative Commons 2.0

Wires can be stripped with any sharp object, but the easiest, cleanest way to get the job done is a wire stripper. Scissors, razor blades, and other sharp objects can also do the trick, but you run the risk of accidentally cutting all the way through the wire or generally making 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 and butt connectors in a pile
flattop341 / Flickr / Creative Commons 2.0

Wire nuts are fine for electrical wiring in your house, but you don’t blow down the freeway at 70mph in your house, or take it down bumpy back roads. Due to the vibration generated from driving a vehicle, even the tightest wire nuts will tend to loosen up over time. In a best-case scenario, that will just cause your device to stop working. In a ​worst-case scenario, something might short out.

Use Solder or Butt Connectors

Wire solder in a spool
Windell Oskay / Flickr / Creative Commons 2.0

The best way to complete any DIY wiring project in your car is with a soldering iron and electrical grade solder. If you know how to solder, and you have the equipment, there’s no better way to get the job done. A good solder joint will stand up to routine vibration and protect the 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. You use them by stripping the wires you want to connect, sliding the wires into the butt connector, and then squeezing it with a crimping tool. This is the easiest way to wire any new electronics, but you will need a crimping tool to do it right.

Insulate Your Wire Connections

Spool of heat shrink it insulate wired connections

The last, and possibly most important, DIY wiring tip is to properly insulate your connections. Whether you use solder or butt connectors, proper insulation will help make sure 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 have to 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.

Be careful not to melt the heat shrink by touching it with the soldering iron.

Electrical tape will also get the job done, but you have to make sure to use a high-quality product. If you use low-quality electrical tape or other kinds of tape, it may peel off, crack, or wither over time.

Was this page helpful?