Im working on a sound system for my 1990 525i and I was wondering if anyone knows if and where there is a hole in the firewall to pass the speaker wires through. also, if there is any way other than passing the wire through the back seat other than through the speaker hole. (other than cutting for the time being)

Hello,

I ran my wiring through the ECU container on the passenger side, there are grommets already there, then they hide in the ECU box and go through a ruber boot that leads to behind the glove box and then down.

If you remove your backseats backs completely, on either side (driver or passenger) toward the bottom you'll see black rubber grommets that are there, just punch out the size you need and rub your wire through there... easy as that :)

Good luck! :)