Fog lights work best mounted in, on or below the bumper (10 to 24 inches above the road surface) or anywhere below the center of the headlights, where their beam can cut just under that of the low-beam headlights.
Fog lights should be positioned closer together than the headlights (approximately 20 to 26 inches between them) and aimed so the cut-off line of the beam is about the middle of the low-beam headlights’ pattern.
The best way to aim the lights is to park the truck on a level surface 25 feet from a wall. Measure the distance between the center of the fog light and the ground.
Place a horizontal mark on the wall at that height.
Now adjust the lights so the top of the beam pattern is about 4 inches below the lamp center at 25 feet with the lamp facing straight forward.
If you drive over a lot of narrow, winding country roads, angle the passenger’s-side light slightly to the right of the low-beam headlight’s center so the fog light illuminates even more of the road side.
Also make sure they are wired so they operate either independently and/or in conjunction with the low-beams to keep within the legal requirements.
Never use fog lights with high-beam headlamps or auxiliary driving lights as this can blind oncoming traffic. — Bruce W. Smith