Ok. Would you have a rear view of the unit that shows what each jack is for or an old user/owners manual?

It’s ok. I think I figured it out anyway. Looking at the unit from the back, it appears the top right jack is low level input with the bottom right jack as a low level line out or “monitor out” which you would plug into the input of a guitar amp. When talk box is switched “active” using center foot switch the line out is muted. The input is extremely sensitive, so using that as say in an effects loop would be over-powering for the internal amp & driver.** Therefore you’d likely plug in just a guitar direct or perhaps after a distortion pedal of sorts. When the talk box is switched “off” the signal is sent out to the line out jack. The right side foot switch is for using the internal amp to switch between the internal driver and the rear right side jack (next to the power cord) as a speaker out making the unit a stand-alone type device. Whoever originally wired this up must have been smoking some serious ganga! Nothing had any conformity as far as color coding of wires. White, red & green could all be ground. Red could be +voltage,

**I’m thinking of incorporating a -20dBV line level pad switch circuit at the input so it could be used with an effects loop with the permission of the owner.