This is a "how to" to install fog lights using factory assemblies and the factory switch..
You will need:
Cheap aftermarket fog light wiring kit, I bought mine at autozone.
1 relay
lengths of wire
blade connectors, bullet connectors, and a crimp tool.
I used this diagram to wire it up...
The only thing I didn't wire up is the "indicator" though, I'm not sure if thats the wire that would go to illuminate the cluster light.
One thing you will need to know is how to route the wire from the engine bay into the passenger compartment.
There are 4 T-10 screws in all four corners of the fuse box... The rear ones are a major PITA to get out and back in, so take your time. Once you have that up, or at least loose, so that you can raise it up, go inside the car and remove the lower panels on the drivers side dashboard. once you have them off, use a wire coat hanger that you form into a u shape, and push the U shape through the wire pass through which is located in the upper left corner of the firewall, you see the big loom of wire so it's easy to spot.
Once you see the hanger on the other side in the lower portion of the fuse box, pass your wires through.
In the foglight diagram above, it says to run one wire from the switch to IGN or battery power/fusebox. Instead, since I only wanted the switch to function when the Headlight switch was on, I tapped into a wire on the Headlight switch harness. I believe it is yellow/beige (This is different on other model years, mine is a '95), but not 100% sure. it is on the end of the connector, next to a red wire, and it's a thicker wire.
Once you have it wired up that way. the fogs will only come on when you have the headlight switch on, just like factory. Also they will shut off like the headlights when the ignition is off..
Note! To illuminate the gauge cluster indicator for the fogs splice into the wire that is going from your Fog light switch to the relay, and run a length of wire to connector position 8 on the blue X17 connector in the gauge cluster harness. you may have to get the proper lead pin at the dealer for this to work, or a cut one off a parted out BMW.