Rewire your pre-'94 foglights independent of the headlights
Remove the fuse panel and use the diagram on its reverse to locate the 15 amp fuse assigned to the fog lights. On my '89, the location is fuse #15.
Detach the fuse board from the dash using a 7mm socket on the two screws located at the upper-left and lower-right.
Push the fuse board in and tilt to gain access to the blinker module (the large metal cylinder in the corner) and remove it.
With the blinker module removed (to allow more room) gently pull the fuse board out of the dash, taking care not to damage any wires or connections.
Detach the left control switches that regulate the headlights and foglights from the dash by pulling on the left-hand side and using a small screwdriver to push in the two holding tabs.
The lower switch controlling the foglights should have two wires extending out. Note the color of these. For example, LB/BK, a light blue wire with a black stripe.
Reinsert the switch assembly into the dash.
On the back side of the fuse board, locate the two wires extending from the fuse that cooresponds to the foglights (#15 on my car). One should match one of the wires on the switch. On my car, this match was the LB/BK wire as described above.
Cut the OTHER wire from the fuse (BK/R, black with a red stripe on mine) about (2) two inches from where it enters the fuse.
Using a wire cap, secure the half of the wire that is NOT attached to the fuse.
Use a wire stripper to expose about 1/4" of wire on the 2" segment.
Connect the 2" segment to one of the unused ports. Here you have a choice to make.
If you want the ability to turn your foglights on and off by the switch alone, crimp the end of the exposed 2" segment to a source that is always hot, such as the central yellow hot wire (or so it was made in '89).
If you want the ability to turn your foglighs on and off by the switch but they only come on when the key is in the ACC or ON position (same scenario as for your radio and power windows), then crimp the exposed 2" segment to the source that is hot only when the key is in those positions, such as the left black hot wire (again, in '89).
Enjoy your new-found freedom of foglight control but drive responsibly.