Fog Lights are probably one of the most popular aftermarket upgrades for a car. They're also one of the simplest. Here's how to run them off of a switch:
1: Find the location for where the lamps will be mounted. If holes need to be drilled, drill hole(s) that will line up with your fog light mounting bracket. After you have your holes drilled, make sure you will have enough clearance to run the wires behind the lamps. Mount the brackets(don't mount the lamps yet)
2: Now, run your 12 volt power supply from the positive side of your battery to an in-line fuse, 30 amp. This wire should be no larger than 16 gauge. Before you have everything installed, keep the fuse out of the line so that you don't ground out your battery on accident. Run your whole power supply wire to where ever you have designated the switch to be and cap it off with a female spade end.
3: With your ground, you want to have it be no longer than 2 feet long and no bigger than 16 gauge. You also want it on bare metal. No painted metal, as painted metal will cause an inconsistency in the current flow, and will cause the lights to not work all the time. So after you've found a place with bare metal, bolt your ground wire down, and run it to your switch. Cap it off with a female spade end.
4: Along with your power supply and ground wires, your light turn-on wire should be no larger than 16 gauge. This is the wire that runs from both lights to your switch. With this, you want to cap off an end with a female spade end, and connect it to your switch. Get all of the interior wires installed and hidden, and then run your turn-on wire from the switch to your lights. This is the fastest and easiest way to get the correct length. Run your turn-on wire to the first lamp, and depending on the end of the lamp wire, cap the wire off with whatever cap necessary. When you cap it off, put another end of wire into the cap as well, to run to your other light. Cap it like this:
5: After you have both turn-on wires hooked up to your lights, you can usually ground them to the bolt(s) that hold the bracket in. This is the easiest way, but if it's not an option for your car, then find somewhere that's within 12 inches of the light itself. When you have the ground and turn-on wires hooked up to your light, install your light into the bracket. Put your 30 amp fuse into the power supply line, and you're ready to go!
Here's a simple diagram to go by:
Tips: To make it look professionally done, make sure to hide all of your wires. If you have to run any wires under your hood, or anywhere else on the exterior, wrap them in wire loom to protect them and for aesthetic purposes.
If you have any problems such as only one light turns on, or neither light turns on, etc, check your connections on the lights themselves, and on the back of the switch. These are the most common problems. Also, check all of your grounds. If only one light works, check the ground for that light. I've had that problem numerous times, and it's a really quick fix.
If you have any questions, feel free to ask. I wrote this myself, so there's no source to cite.
