Looks different than the usual Stereo Jack... Ring and Sleeve used to turn on batt.
https://images.app.goo.gl/p4vWMHLsTzHiosvm9
From a google the 4 Wire MM hack switches the Pos
Out of Stock Strings and things... Discontinued say others.
Someone is looking to order some odds n sods via USA... get on their case to include a jack socket etc.
I'd rewire and switch the neg and go for a Pure Tone Multi Contact Stereo...
Got a Rowin Nano MXR Phase 90-a-like.
Speed Control w/ Vintage (Script) / Modern (Block) Switch
Looks Super-Dinky next to my CB Bass Wah.
Same size as the Joyo Iron Man Series, but without the flip lid.
My Aria Pro Jazz is 21 with an overhang.. not total on the heal compatability.
Few candidates on the bay..
Vintage Maple 'n Blocks?
https://www.ebay.co.uk/itm/204882815993?
Update: Twas the jack sockets... sealed 7 or 9 pin units.
Think the IP is grounded with no jack they were worn so wouldn't un-ground.
The Board Sockets had a different pin out, so Chassis mounted the sockets (upside down for room) and fly-wired to the board.
Need to give it a proper go.