How to Install Head Lights With a Relay Switch


Whether it's for a hot rod, dune buggy or old woods truck, there's only one correct way to wire headlights and that is to use a relay switch in the circuit. Using a relay insures brighter headlights, while retaining the ability to use lighter wiring and a simple toggle switch to control the headlights. The use of two relays and a double throw toggle switch will allow the use of high- and low-beam headlights.

Things You'll Need

  • DPDT toggle switch
  • 16-gauge automotive wire
  • 14-gauge automotive wire
  • Signal Stat 192 relays
  • 20-Amp automotive circuit breaker
  • 12-volt LED and socket
  • Solderless connectors
  • Solderless connector crimping tool
  • Self-tapping screws
  • Electric drill
  • Socket to fit self-tapping screws
  • Chose a location under the hood to mount the two relays and the 20-amp circuit breaker. The inner fender or radiator support are good locations. Mount the relays and breaker using self-tapping screws. Drive the screws using an electric drill equipped with a socket.

  • Cut a length of 14-gauge automotive wire long enough to reach from terminal 85 on one of the relays to the headlight farthest from the relay. Cut a second wire to extend from the same terminal to the closer headlight.

  • Strip 1/4-inch of insulation from the ends of both of these wires. Crimp a female spade type solderless connector to one end of both wires. Then crimp the other end of both wires into a third solderless connector. The wires will look like a lopsided "Y" at this point.

  • Plug the connector with the two wires into it on relay terminal 85 on the relay. Plug the other connectors on the high beam terminal of both headlight bulbs.

  • Make another wire to connect the low beam terminal of both headlight bulbs to terminal 85 on the other relay.

  • Cut a wire long enough to go from the ground terminal on each headlight to a good ground. Strip 1/4-inch of insulation from each end of the wire. Crimp a female spade connector on one end, and a solderless ring connector on the other end. Attach the end with the ring connector to the vehicle with a self-tapping screw. Plug the female connector on the ground terminal of the bulb. Repeat this step for the second headlight.

  • Using 14-gauge wire and solderless connectors, connect terminal 86 on both relays to one side of the 20-amp circuit breaker. Connect the other circuit breaker terminal to the positive terminal on the starter solenoid.

  • Using 16-gauge automotive wire and solderless connectors, connect relay terminal 30 on both relays to a good ground. The mounting screw for the relay is a good location to connect the ground wire to the vehicle body to accomplish a ground connection.

  • Mount the DPDT toggle switch in a location within easy reach of the driver. Connect the center terminal of the switch to a fused 12-volt circuit using 16-gauge wire.

  • Run a 16-gauge wire from terminal 87 on both relays to the toggle switch. Connect one to each of the two remaining switch terminals using solderless connectors. Connect the lead from the 12-volt LED to the same terminal on the switch as the 16-gauge wire from the high beam relay. Connect the other LED lead to a good ground.

Tips & Warnings

  • Always disconnect the vehicle battery before doing any work on a vehicle electrical system.

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  • Photo Credit Photo by, Graphics by KKLowell
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