2003 Mustang radio install

[94chirps]

Hello I have a 2003 Mustang GT with the Mach 460 I'm installing a double din radio the previous owner had a single DIN installed and it worked great but I can't figure out where to put the two RCA wires but come from the factory amp the front speakers cut-out at half volume if I turn it down a couple of notches they turn that back on must be the app any help would be appreciated I don't know where to plug these things in do I need a y splitter and use the subwoofer input???