How to Wire Driving Lights Into High Beamby Robert Moore
A major consideration when installing aftermarket driving lights is having to drill, or cut a hole somewhere inside the vehicle for the switch and interior wiring. If you wire them into the existing headlight circuit, you can skip the included switch, and keep additional wiring to a minimum. The most important thing to remember is that you must wire them in parallel, as opposed to in series, to prevent overloading the existing circuit. If you choose to wire your lights into the existing high-beam circuit, they will only operate when the high beams are on.
- Wiring the driving lights in series with the existing circuit may result in excessive amperage draw across the circuit, which may cause a fire.
- In most states, it is illegal to have more than four, forward-illuminating lights on at one time. Before wiring your new lights into the circuit for your high beams, make sure the low-beam headlights turn off when the high-beams are turned on.
Items you will need
Memory saver unit
Service manual or repair manual
Wire diagram for your specific year, make and model of vehicle
Thin pick tool
Heat shrink tubing
Install a memory saver
A memory saver unit will provide power to the on-board computer and the radio to prevent memory loss when the battery is disconnected. Follow the instructions included with the unit to install it properly.
Disconnect the battery
Disconnect the negative battery cable with a battery wrench. Isolate the cable so that it cannot come into contact with the negative battery terminal during this procedure.
You run the risk of electrocution if you do not disconnect the battery before proceeding.
Remove the bumper and headlights
Most front bumper covers are secured by a number of push-pin retainers on the top and bottom of the cover, as well as a couple screws in each wheel well. There are occasionally addition support brackets hidden behind the front of the wheel wells, depending on your make and model. Once the bumper is removed, you should be able to remove the bolts for your headlight assemblies. Disconnect the wiring harness from the bulbs, then set the assemblies aside.
If you have enough room to work, you may not need to remove the headlights. For help removing the bumper and/or headlights, refer to your service or repair manual.
Route the power supply wire
The power supply wire will run from the high-beam relay wiring harness to the driving or fog lights. Start by taping one end of the power wire to the metal bumper support. Leave at least one foot of wire hanging after the tape to leave enough slack for the connection to the lights. Route the power wire toward the fuse box that contains the high-beam relay. Conceal the wire in existing wire looms as much as possible as you route the wire. Make sure it isn't in any place that will be rubbed or pinched as you drive. Once you've routed the wire to the box, cut the wire so that there is only enough to connect it to the wiring harness for the fuse box with a few inches to spare. Zip strip the wiring to the bumper support and other places as needed to secure the wire so that it cannot move when driving.
Access the wiring for your high-beam lights
Disconnect the wiring harness from the fuse box.
If you cannot access the wiring harness the way the fuse box sits, consult a service or owners manual to learn how to access the wiring harness.
Refer to your vehicles wiring diagram and determine the color of wire and pin number of the power supply wire for your existing high-beam headlights. If you have two headlight relays, you can choose either one.
Remove the wire from the wiring harness
Look into the connector end of the wiring harness. Locate the pin for the high-beam power supply wire -- double check your selection by verifying the wire color. Use a small pick tool to push down on the small locking tab on the metal connection pin, and pull that wire out of the wiring harness connector.
Connect the two wires
To run the power supply in parallel, splice the new wire into the existing wire right at the base of the pin on the existing wire. Trim one inch of insulation from each wire with the wire trimmers. Twist the new wire onto the existing wire, then slide a piece of heatshrink tubing over the new splice so that it covers all of the bare wire, but not the pin on the existing wire. Warm the heatshrink with a lighter or heat gun until it shrinks and seals the new splice. Push the pin back into the harness connector and listen for a click as it locks in place. Give it a gentle tug to make sure it is secured. Plug the wiring harness into the fuse box, then mount the fuse box to the vehicle, if previously removed.
Connect the power supply wire to the new lights
Trim back an inch of insulation on the wire for the light closest to the fuse box. Slide a piece of heatshrink onto one of the wires, then twist them together. Apply heat to the heatshrink to seal the connection. Connect the second light to the first light according to the instructions that came with the lights, if they didn't come permanently connected from the manufacturer.
Most aftermarket lights are run in series and and connect together. The included wiring also has connectors on one end of the supply wire and on the wires that are attached to the lights. Use the connectors as opposed to cutting them off and making a twist connection.
Make the ground connection
Look around on the bumper support and find one of the body grounds. Remove the bolt that secures the ground wires. Slide the eyelet connect on the light's ground wire over the bolt, followed by the OEM eyelet connector for the ground wires at that location. Install and snug the ground bolt.
Most aftermarket light kits are run in series, so you'll likely have a single ground wire.
If there isn't a ground location close enough, you can drill and tap a new hole in the bumper. Just make sure there is bare metal around the hole to ensure a good ground connection.
Put the car back together
Install the headlights and connect them, if removed, followed by the bumper cover. Refer to your repair manual and torque all bolts to specification. Install all push-pin retainers in their respective places.
Plastic retainers are damaged easily when removed. You can obtain replacements at most parts stores, if needed. Make sure to take one with you to the store so you can match it and get the correct ones.
Connect the battery
Connect the negative battery cable to the battery. Snug the connection, or tighten it according the torque spec listed in your repair manual. Disconnect the memory saver by following the instructions that came with it.