preamp?

[Dennis Moyer]

I been trying to find out whats the best way to wire a preamp into this bass

the pickups are as followed

coil structures:
bridge: humbucker
mid: split coil
neck: single coil with hum cancelling.

I have read that simular basses had a 9v Bartolini preamp installed, i believe this one
has had it removed. either way installing a new one that will work with my pickups and
best suited is the goal.

 

[Doctor J]

What do the three switches currently do?