I don't think he really answered your question, and well, it's been months since you asked, but basically the idea is to find the firewall penetrations that have already been made by the manufacturer in running wires through the firewall for the steering column, power windows, etc. Your owner's manual should help point out these places, but actually feeding the amp power cable through it is very challenging. If you know somebody that has already done it before, they will be of much more help than... me.
Greg, October 2007