379 Factory Amp Wiring?

I'm going to try this here first since there is more traffic. Does anybody know how to wire up a newer radio (its a jvc) in an '02 379 that has the factory amp? I have the correct harness for the year, but it doesn't match. There is just one big square plug that goes into the taped up main harness that runs into the amp, not the 3 little plugs. I would like to keep the amp and have a radio with an aux in plug. Oh and the radio that's in there has the antenna wire cut off 6' from the radio but it still get perfect reception? Can anybody point me in the right direction?

 

I think so, I'll have to go look at it again. I think I may be overlooking something obvious.