If u are going to buy one from the top end of the market, then it will most likely come with a brain which is normally no larger than a large bar of chocolate (U.K. Chocolate..lol). This can be mounted under the seat as the wires are only about 1-1.5 mtrs in length, or mount in Glove box. U have your usual power 12v (in sum cases X3 i/e ACC, LIVE ALWAYS and Illumination), and ground (normally only one lead). Usual set of either 8 or 4 wires for 4 or 2 speakers, most cases RCA output for amp/sub amp.. of course not forgetting the wires connecting yur head unit to the Brain. If u are mounting one of these babies, make sure u have plenty of space for the wires to run behind the head unit. Hope that helps!