Fog lights wiring instructions

Written by rusty noble
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Fog lights wiring instructions
Fog lights help you see at night. (fog lights on suv image by Kathy Burns from

Fog lights are wired similar to headlamps. They must be fused and run through a higher current relay to avoid high current through the fog lamp on and off switch. Fog lamps typically will use eight amps of current for the pair, but the relay will draw only about 0.3 amps from the switch. Fog lamps should be mounted as low as possible to illuminate the road while reducing reflection back from the fog.

Skill level:

Things you need

  • 18-gauge wire
  • Headlight relay or other 12-volt relay with a rating of 30 amps or more
  • 20 amp in-line fuse assembly
  • On and off switch

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  1. 1

    Connect a wire from a switched 12-volt source on your fuse panel to one terminal on the on and off switch.

  2. 2

    Connect a wire from the other terminal of the on and off switch to the control terminal of the relay.

  3. 3

    Connect a wire from the ground terminal of the relay to chassis ground on the automobile.

  4. 4

    Connect a wire from the 12-volt terminal of the battery to the in-line 20-amp fuse.

  5. 5

    Connect a wire from the in-line 20-amp fuse to the common terminal on the relay.

  6. 6

    Connect a wire from the normally open terminal on the relay to each of the two fog lamps.

  7. 7

    Connect a ground wire from each of the fog lamps to the automobile chassis. Some fog lamps are internally grounded through the mounting hardware, but hard wiring the ground will prevent intermittent operation.

Tips and warnings

  • Wiring can be soldered, but using crimped connectors and terminals is an easier way to do automobile wiring.
  • Make sure the ignition is off when connecting wiring. Wiring with power applied can result in sparks that can ignite flammable vapours in the engine compartment.

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