You can connect LED lights to a car for added nighttime safety, or just to dress up the appearance of your vehicle. Almost all aftermarket LED lights sold in auto stores today have a simple, single-wire installation. You will need some basic know-how about splicing electrical wires to install LED lights on a car, but it's a fairly simple process. As an example, we'll walk you through how to connect an LED light bar, and you can then apply these steps to any kind of single-wire LED light.
Disconnect the negative cable from your car's battery.
Open the boot of your car and look for the wiring harness that leads to the rear lights. You may have to use a flathead or Phillips screwdriver to remove any covering panels to access the lights. Older model cars will have wires passing directly and simply through the body of the car.
Identify the "earth" wire feeding into the rear lights. The "earth" wire is the wire that feeds power to the lights from the fuse box. You can identify this wire from wiring diagrams for your car, by tracing the wire from the fuse box to the light, or by the process of elimination--trace the ground wire from the lights to the frame (usually near the light assembly), and the earth wire will be the other one coming off the lights.
Cut the earth wire in two. Make sure you do this at least 4 inches away from the lighting assembly or any point in which the wire passes through the frame of the car or joins a major part of the wiring harness. This will make the wire easier to work with.
Strip a half-inch of the plastic wire coating off both ends of the earth wire. Strip one end of your 16-gauge wire. Twist all three ends of bare wire together tightly and then wrap the connection in electrical tape.
Locate where you want to mount your LED light bar on your car. Make sure there is a point at which you can pass the single wire from the LED assembly through the body of the car and into the boot (whether you are installing on the interior or exterior). You will add length to the wire if necessary, but try to maintain the shortest distance between the earth wire of the LED bar and the earth wire of your lighting assembly.
Follow the instructions that came with your LED lights to attach them to your car. Some models screw down, and some also may require the use of an adhesive or additional clips.
Pass the earth wire of your LED lights through the body of your car to the boot. If your location is too far away to allow the wire included with the LED light to reach, feed the wire you attached to the earth wire of the lights up through the body and then splice it to the LED wire. If your LED wire reaches, splice it to the 16-gauge wire in the boot.
Tape the earth wire up and out of the way of boot hinges or payloads. Using a couple wraps of electrical tape around the wire to hold it to the original wiring harness is always a good idea.
LED lights work by providing a ground for the LED through the frame the light is mounted in. If the frame is not making good enough contact with the body of your car, use 16-gauge wire to create a ground wire, attach it somewhere on the frame of the LED lights, and run the wire to a bolt on the metal frame of the car.
Never work on any part of the electrical system of a car without first disconnecting the negative cable of the battery. Even a small LED light connects to a power source that can cause a severe shock.