It does plug directly in to the radio, but the Volvo cable required an additional splice. THe Volvo cable has a square pin plug on the end and the 2 wires branch off that require splicing.

The adaopter is not an amp at all, it just converts signals from stereo output and iPod back and forth, probably a little computer chip in there. It is made for Honda stereos but works with 98-2000 Volvo stereos with the additional VOlvo cable I mentioned - that requires the batt and acc wires.

There is another product for newer Volvos.

The RCA inputs are for optional additional inputs such as satellite radio or whatever you want.