Okay, found the showcase thread for Dave's 3 pickup Essence.... Interesting way to wire a 3 pickup bass.
"Three position Q switch; and a three position pickup selector switch. Plus the regular volume, pan, and filter. Apparently, the bridge pickup is always on and routed to one side of the Pan. The selector apparently chooses between the neck, the mid, and what appears to be the sum of the neck and mid. That choice is then routed to the other side of the Pan. Lots of tone choices!"