You know, looking at this again, I think you might need to send it in here for servicing. There should be a grey shielded wire between the volume harness with the cut wires to the 2-prong connector on the filter module.
The battery clip is MUCH newer than the rest and doesn't plug in to the connector you have it next to. On this system, the battery clip would have been hardwired to the volume harness and output jack. The jack is a Switchcraft L113 and not a standard jack (it need to turn the battery on).
There's no charge to test, and if everything works out OK on this system otherwise, the jack is $12, the labor will fall in the $35 minimum bench charge.
If you want to send this in to me, just email me (in my profile) with:
1. your name and return shipping address
2. phone number(s) / email to contact you
3. the amount you want us to insure the parcel for when we send it back to you
I'll let you know when we get it.