OEM foglight installation in a Sport

If you build your harness you don't have to use a relay as long as the switch itself and the wires to it have sufficient ampacity. For 2, 55 watt lamps you will probably want to use a 30 amp switch and 12 AWG wire for reliability and minimal voltage drop to the lights. A relay is a good idea because the main power run to the lights can be shortened and a compact little swtich that might not have much ampacity can be used. Also a relay or relays allows you to set the conditions for the fogs to be enabled, if you want, and you don't have to go off a select part of the existing fuse block.

For example, I usually just use one 30 amp, 12 volt relay that takes power from one of the clearance markers or parking lights, then through the dash switch, and back to the relay coil. That way I won't accidentally leave the fogs on, on some gloomy day, and find a dead battery. Power could be taken off the fuse block where power is only present with the ignition on and no need for the relay, but messing around in the tight quarters of the fuse block and trying to add a circuit is usually more trouble than installing a $6 relay and having a shorter power run to the lights with it anyway.