Battlemaul

Hi, I have a 2001 GS300, and my sub has not been working since I bought the car 4 months ago. I have run a voltmeter and the sub had no voltage. I have tested my sub with a AA battery, and it works. I bought another amp to see if my amp was the problem, and my sub still doesn't work. I do not know what the problem is, I think it may be wiring. I will post photos of my sub. I bought the car with an aftermarket stereo (Kenwood dpx500bt), but stock sub and stock amp. I think the problem may be between the amp and sub, or stereo to the amp. Is there a good way to test the stock amp? What could the problem be?
https://imgur.com/gallery/p3iRjJ6 (photos of my sub)