I currently have my Big Rig in the P position of a passive Fender-style fiver... neck J pickup location is probably more accurate. I first had it wired in series which made it mid-focused. It's now wired in parallel for a more balanced tone, but output is significantly lower than my other basses -- and I'm mainly referring to my other passive basses, one having the NP5V (vintage alnico P pickup) and the other with Big Splits. In series mode, the Big Rig was comparable in output to those.
I'm thinking Big Rig in series might be the bomb on a fretless, but I don't own one... gotta have speed bumps on my necks.