Stock Sub does not work

[SHOGUN88]

I have the stock jbl sound system and have always asumed it all worked but i checked and the sub does not work. The previous owner did something weird with the sound system there are a million wires everywhere, it doesnt look like he had differnt speakers in since i replaced the front ones and it looked like it was never taken apart before. There are a bunch of wires running to the front of the car, head unit? Basically what it looks like is done is the connector that goes on the right side of the black amp is mostly cut and wires are spliced in that go to the speakers, the connector on the left side is unplugged. The only wires that are connected are 2 black and green wires that come out of the top to the black harness, so is it even running off the amps? On the sub amp the sub was plugged in on the left side but it clearly does not work. I took it apart and it is not blown it looks brand new. There is also an aftermaket head unit he installed. Its hard to explain since im not to good with electronics but hopefully somebody can help me sort out this mess, or basically what i need to do to make this all work together.