This is the right way to wire a set
of fog lights. The relay switches the heavy current to the fog lights with
big wire, while the dashboard switch wiring can be very small. This keeps
high current and large wires out from under the dash and in the engine
compartment where they belong. A typical set of 55 watt lights will draw
about 8 amps for the pair. The dash switch will pull only about 0.3 amps
to operate the relay.
Fog Light wiring using a Bosch relay
Be sure to run extra ground wires
from the fog lights themselves. Don't depend on the cheap spring or case
ground to work. Take the light apart if necessary, and add a real ground
wire. Run these to the frame somewhere handy. This will keep the lights
from being intermittent.
This diagram shows the wiring
using a Bosch relay. These are found just about everywhere.