FWIW:
Interesting cause those wires don’t seem to flow with the removal of the preamp. Pup leads, jack (only cause it‘s flushmount), and bridge ground are all that is required. The entire harness then pulls from the control bay.
On the surface it sounds like a probable easy fix - most of the preamp is wired. Mere speculation and you could possibly smoke the pre finding out but:
1) to battery hot lead
2) ground (ties with 4) or neutral ties with battery negative
3) to jack hot terminal (tip)
4) to jack ground
You need a meter to verify what terminals are what on the jack and what the switch is doing. The nuetral terminal will not have continuity when you touch the other meter lead to the outside face of the jack, the ground will (no cord in jack). The hot terminal will show continuity when you touch it with the tip of a guitar cord plugged into the jack.
Also you can take a magifying glass, get in some natural light and compare the loose ends and their probable contacts - you'll likely be able to figure out one or two of the connections from that alone.
A local tech would probably do this for you for $15 or $20.
Here's some other food for thought:
DIMENTO'S BASIC TROUBLE-SHOOTING GUIDE
Anybody else?
