Picked up an OEM sub and amp...need help with wiring

[PimpClayR1]

Let me start by saying I have an 01 Explorer Sport. Came with basic sound. I was at the local junkyard looking for some little nic-nac parts and came across a fully loaded 02 Sport. I looked in the rear and saw that it had the factory sub and amp combo! I didn't know the 01-03 Sports had that as an option. I was able to get the sub and amp box out and picked it up for $20! Couldn't pass up that deal even if I just use the box to hold a sub in the stock location. I traced the amp wire to the black connector plug behind the passenger floor kick panel. I unplugged the connector and when I got home. I saw I had the gray plug in my truck but no where to connect the black one to. I assume that was the plug that would have come from the radio to amp. I went back the next day to try and trace it down but couldn't seem to find it. Looked like it was all interconnected to the main wiring harness for the vehicle and not just the radio plugs. My ex came with a single cd player and didnt have premium audio at all. I worked at an auto auction a couple years ago and swapped my HU for one out of a Ranger b/c it was a factory Pioneer 6cd in dash. Sorry for the long write up....just trying to give as much info as necessary. I wanted to know how I could go about getting the plug I would need to wire up the sub and amp to the stock HU. I've had the whole custom setup in there before but, its all gone and I just want a little more sound than my 4 speakers have now. I had 2 15" Orion HCCA subwoofers with an Autotek amp, Pioneer 7" flip out...all the bells and whistles lol. Don't want to spend the money to do that all over again, so I'd like to give the stock unit a try. If anything, I will upgrade the sub later on. Hopefully someone can help me figure this out. Thanks in advance guys!!!!