05’ Mariner sub install

My lil brother has a new Mariner(Mercury's version of a Ford Escape) and wants to hook up his subs. He has the Mach audio system which is where my question starts. I looked at the input to the factory sub amp and I see 5 wires coming in. 2 of them are larger than the rest and judging by the fact that they push the sub out (or in depending on which way you hook them up) that they are the power and ground gor the amp. 1 wire is blue and the other two are the same color just with a different color stripe. I'm guessing the blue one is a remote and the other 2 are the signal wires. I hooked up one sub directly to the two wires that I thought were the signal wires and didn't get a sound out of the sub. Would this be because the signal from the factory HU isn't powered? Would it be just as easy to hook up my lineout converter to output side of the factory amp? It has 2 sets of wires going to the sub which I'm guessing is a dvc factory sub. Thank you to everyone who sat here and read this long *** question. Thanks in advance for the replies.Pioneer DEH-P980BT, Zapco DCREF1000.4,Pioneer TS-C520PRS, Adire Extremis, MTX TA91002, TC Sounds TC-3000 15"

I did a search and found a related topic about this install, but in a Ford Escape.Pioneer DEH-P980BT, Zapco DCREF1000.4,Pioneer TS-C520PRS, Adire Extremis, MTX TA91002, TC Sounds TC-3000 15"