subwoofer wiring

Hello everyone, I have a 1999 LX470 with a Sony AX-3200 head unit and a Kenwood KAC-D3104 amp that was installed by the previous owner. It had the nakamichi audio system originally if that matters. Since I bought the car, the rear sub has never worked. I’m not very familiar with car audio, but...

Ok ... please no "use the search function" because trust me I have. If someone can link me where I missed it I'll eat crow. I have a drop in 6.5" sub that I am trying to get to work. I cannot test the stock amp because the "always on power" (Red/Black) doesn't have 12v. The ignition (gray)...