I would imagine you could wire a wire that would be a hot wire to the relay off a factory fog light switch.

 

Someone correct me if I'm wrong (there's a good chance I am) but I remember reading that the fog switch is a momentary switch and connects to the bcm.
When I found a set of lights and brackets at the JY, I snipped the fog connectors so I could fab my own harness. Unless I'm wrong, if you connect the fogs the stock way(using the bcm), you may need a bcm flash for it to "learn" the fog lights.
I'm going to be installing mine sometime soon. If I remember, I'll do a write up.

 

Disconnecting any component of the lighting system wiring harness will throw a "B" code because the BCM checks for grounds, but once reconnected and returned to normal operation the code will clear. No flash is necessary unless the BCM is disconnected.

 

I noticed at the junk yard that all the monte's with a 3800 motor had a fog light harness. Does the 3400 motor monte have a fog light harness too? I looked at 8 different cars and 5 of them were 3800 motors. Could I use a harness off a 3400 impala that has fog lights?

 

I don't think the ls's came with fog lights so the most likely wasn't wired for it,but im sure you could grab one of a car that does have a harness and wire it up,but im not too big on electrical stuff,just be careful when you hook stuff up like that,i had separate headlights wired to a switch on my 86 and it caught fir under the dash because the wire would get really hot for some reason,not too sure

 

Okay so I noticed that my original wire harness has 2 plug ins next to the fuse box. All the other wire harnesses that have fog light hook ups don't have the 2 extra plugins on them. What other montes with fog lights have the 2 other plug ins on the wire harness.