Help identifying this type of J Bass

[strawz]

I've got this fretless MIM Fender Jazz Bass I got off of craigslist and I was wondering if someone with more experience w/ j basses could help me identify a couple things with it.

I've never seen a j with the little switch above the volume/tone knobs. It doesn't seem to do anything when I flip it, but it is connected to the knobs. Also, I've never seen a j with these sort of knobs.



http://imgur.com/NPG1C30

http://imgur.com/tjcSu3U,gTvneVt,qtbEOA0#1

http://imgur.com/tjcSu3U,gTvneVt,qtbEOA0#2

 

[millsbass5]

That's a DIY knob installed by a previous owner. It's hard tellin' what it was designed to do.

 

[BenWhoPlaysBass]

Yah, millsbass is right. Seems like a homemade concoction. Maybe it was some sort of eq circuit the owner tried to put in? I dunno. As for the knobs, they're probably just some aftermarket replacement knobs.