[PaulD]

you will have to look around, most newer headunits have aux inputs for some type of MP3 player or the such.

There is a another small wire that connects to the headunits auto turnon wire and the amps turn on terminal, it will turn the amp on and off with the radio. A good 75 watt X 4 amp should be enough to power 2 speakers in the door and 2 speakers in the back. Be aware that 6X9's or 6 1/2's will not have much bass.