How to Install a Relay With HID Headlights

car Headlights
  • 2-4 hours
  • Intermediate
  • 50-100
What You'll Need
Hand gloves
Wire stripper
Screw driver
Marking chalk
HID lamp kit
HID fused relay harness
Electrolytic capacitor, 470uF 35V
Electrical tape
Tie wraps
Small utility table

To install HID headlights as an upgrade, you may be tempted to get the services of the automotive electrician. However, there is a way to do this on your own and save some money on service fees. To install a relay with HID headlights, this is what you should do.

Step 1 – Get the Area Ready

Position the car near the garage wall and switch on your headlamps at low position. Use chalk to mark the lamp beam horizon and the position of your car on the floor. This is important to make sure the HID beam is not higher than your current setting.

Make sure the car engine is turned off and has cooled down. Unscrew and remove the car battery terminals; this is important to make sure you won’t accidentally trigger then ruin your headlamp.

Keep the tools and other accessories on a small utility table for easy access. If the HID lamp kit includes a relay harness, discard this and instead use the fused relay harness as shown in above materials list.

Step 2 – Remove the Existing Headlamp and Install the HID Lamp

Remove the existing bulb by turning it counter-clockwise and pulling it out. Take out your HID Kit and carefully cut the rubber grommet to remove it; be careful not to cut the wires too. Remove the loose wires along with the grommet. Fit your HID bulb into the lamp socket. Warning: never touch the bulb itself—only hold at the base.

Step 3 – Install the Fused Relay Harness and Connect to HID Bulb Assembly

Strip off ½ inch from both the red (one connected to the fuse) and black wires (ground) of the relay harness and crimp into the lug. Fix the red terminal to the positive (+) side of the car battery connector and the black terminal to the negative (-) side of car battery connector. Connect the other wire from the harness with plug to the car’s connector for the original bulb. Watch out for the correct orientation of the connectors: the red wire from the harness should match the white wire from the car’s original plug and the black wire to the black as well. Remove the relay from its socket. Insert the terminals of the electrolytic capacitor directly to the relay plug: the positive side must be connected to the terminal with red wire and the negative terminal (the side of the capacitor with the white marking and “–“ sign) to the one directly opposite the red terminal.

Fix the ballast with tie wraps at the back of head lamp housing; make sure it’s not loose. Connect the longer wire of the relay harness to the farther ballast and the shorter one to the nearest ballast. Connect the wires outgoing from the ballast to the HID bulb.

Step 4 – Finishing Up

Wrap the fuse assembly with electrical tape. Do likewise on the capacitor to the relay housing. Put tie wrap on the loose wires to fix these. Reconnect the car connectors back to the battery. Turn on headlights and adjust light level as marked on the wall.