For this groups info, the ZZPerformance high low fan switch will work for at least all 1997 Bonnevilles. There are a couple of differences in the insructions, but they are minor and I'll help anyone through it if they want my help.
The main difference is the relay setup. The Grand Prixs use three relays and Bonnevilles use two. The reference in their description stating the fans run with the key off is incorrect with the Bonneville system. They will shut off with the key off. Also, don't bother with the timer as it won't work with our setup.