what kind of switch would work?

I am needing a switch that can select two sets of inputs.

What I am doing is cutting the left and right pos and neg wires near the headunit that goes to the back factory Bose amp on my Cadillac.

I need a switch so that I can wire in the factory headunit on one side and wire my iPhone to the other and be able to switch between the two for input to the rear amp. So I need 4 wires going in for the factory headunit and four going in from the iPhone and be able to select either one to go to the amp.

I know shielded cable will need to be used to and from the switch. But what kind of small switch would accomplish this? If now available at Radio Shack, where?

Thanks in advance for any advice folks.