Please note that this is for 94/95 Bonnevilles ONLY:
Remove the passenger side hush panel. Pull the CENTER WHITE connector. Blue on the left, red on the right, white in the center:
In this pic, the rear of the car is TOP, the front of the car is BOTTOM, the driver'* side is LEFT, and the passenger side is RIGHT. You're looking UP, facing forward.
After you pull the connector, you're looking for a dark blue wire in slot D10. One side of the connector ONLY will have a blue wire in hole #10. In these pics, if you look at the top row (not marked, but not the C side), you can count from left to right 1-whatever. My thumb is next to slot 1.
Provide an ALTERNATE ground through a switch for this wire. Don't cut it and leave it dangling on either end. Tap INTO it, providing another path to ground through a switch. When you turn the switch on, the fans will come on high.