How to Wire Fog Lights With a Relay

Updated July 19, 2017

Adding fog lights to your car or truck is a great way to improve your driving safety in rain and fog. Fog lights are mounted low on the vehicle and their wide flat beam of light illuminates the road under the fog reducing light bouncing back in the driver's eyes. It is recommended to always wire fog lights with a relay. This ensures that the fog lights receive full voltage at all times.

Disconnect the negative cable from the battery.

Use a self-tapping sheet metal screw and mount the 10 amp circuit breaker in a location near the battery. Good places to mount the circuit breaker are the inner bumper or the radiator support.

Mount the relay in the same area as the circuit breaker, also using a self-tapping screw.

Run a 14 gauge wire from the fog lights to terminal 86 on the relay. Connect this wire to the pigtail of the fog light with a solderless butt connector and to the relay using a solderless female spade connector.

Connect a short wire from terminal 85 on the relay to terminal 87a. Make your connections using solderless female spade connectors.

Mount a SPST toggle switch in an area easily reached by the driver. Connect a wire to the centre terminal on the toggle switch using a solderless female spade connector. Run this wire to a metal part of the under dash area. Use a self-tapping screw and a solderless ring terminal and attach this wire to the metal. This needs to be a good connection, so make sure that there is no paint under the terminal.

Run a wire from the toggle switch to relay terminal 30. Use solderless female spade connectors on both the switch and the relay.

Connect relay terminal 87 to one of the circuit breaker terminals. This will require one solderless female spade connector and one solderless ring connector.

Connect the other terminal of the circuit breaker to the positive terminal on the battery.This will also require one solderless female spade connector and one solderless ring connector.

Reconnect the negative battery cable.

Things You'll Need

  • Fog lights
  • Automotive relay such as a Signal Stat 192
  • Solderless insulated female spade terminals
  • 10 amp automotive circuit breaker
  • SPST toggle switch
  • 14 gauge primary wire
  • Solderless butt connectors
  • Solderless ring connectors
  • Self tapping screws
  • Solderless connector crimping tool
  • Wire cutters
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About the Author

K.K. Lowell is a freelance writer who has been writing professionally since June 2008, with articles appearing on various websites. A mechanic and truck driver for more than 40 years, Lowell is able to write knowledgeably on many automotive and mechanical subjects. He is currently pursuing a degree in English.