Hey, Just installed an amp in my r32 gtst other day, ok.
OK this what 2 do, on the drivers side the wires going into like a foam rubbery thing, rip that out. now. You'll find a ruber gland.Now whip around inside of the car and, (first get a coat hangar) now Pull back some of the sound deadening stuff( behinde accelerator) , don't need to take it off. Just pull back untill u find it. Might be easier to find if u poke coat hanger through the other end first if u can find it.
U should be able to find the other end of the rubber gland. Once u find that poke the coathangar through (from inside to out / under hood). Move it around a bit, It's very thick. Now once through, rip under the hood and pull the coat hangar out a little more. Now u need some electrical tape / or some tape needs to be fairly strong. Now put the wire side by side to coat hangar (needs to overlap coat hanger and wire) Wrap electrical tape around the wire and coat hanger. Make sure the electrical tape goes up past the wire up the coat hangar and it's makes a smooth like shape sort of when the wire starts up beside coat hangar.
Now Once that's done yank the power wire through the firewall. Now I ran my amp on the back of the seat in my r32, replaced the stupid plastic panel crap thing that sits at inside end of boot with a wooden one, made some brackets of off the two holes that come of the metal near back seat and mounted the wood on theire. On that is my amp and Fire extinguisher.