Years ago, I replaced the stock elctronics in my Fender Power Z Jazz Bass Special with the pickups you are talking about. I used this bass for years in a variety of applications, and got great versatile sound. The short answer about what the switches do is......they change the sound! Here is some info on these PUP's from
www.seymourduncan.com :
Functions of switches on old-style "Active EQ" bass pickups
We stopped making the switch pickups ("Active EQ") in the mid-'90s. We replaced them with the Pro-Active? series.
The little rocker switches on the Active EQ pickups change the sound. Switch #1 shifts the coil resonance. On a Jazz Bass? neck pickup and a P Bass? pickup, the resonance moves downward from 22 KHz to 6.4 KHz. On a Jazz Bass bridge pickup, it move downwards from 17 KHz to 4.9 KHz. The effect is to give a more focused sound with a harder attack. Switch #2 gives a broad band bass boost of 4 dB for the Jazz Bass neck and P Bass pickups, and 5 dB for the Jazz Bass bridge. The switches can be a very effective tool for changing the tonal "character" of your instrument.