Im trying to find a good location to route my power wire through the firewall. Anyone know a good spot? It's a 240 wagon. Thanks

 

right under the left side hood hinge should be a rubber plug with some 'nipples' you can cut off to feed a wire through.

see red wire here. this was several years ago, but I seem to recall poking it through from the driver side and then fishing it out and feeding it around the strut tower alongside a bunch more wires, to connect it to the 'positve terminal' on the relay bar.

 

Problem solved. Thanks Pierce

 

FWIW (about $0.002), while I've always routed my stereo wiring along the drivers side door sill, between the carpet and the rocker, I saw a document from Volvo that said to route stereo etc stuff down the right side of the transmission hump, to the left of the passenger seat. I think maybe this was because there's no factory wiring there, so it will get less interference.

Frankly, since in-dash decks started coming with 50x4 class D amplifiers built right in, I haven't installed an external amp except maybe for a sub (and the last wagon I put a sub in, it was always getting in the way). my current car, a 1992 740, I put 6" component speakers (JL Audio) in the doors, and run them directly off an alpine with '50Wx4' (yes, I know, thats 50W of 'music power', not RMS dc to daylight, but its still plenty to drive speakers at any sane volume). Had to spend quite a bit of time fixxing high volume buzzes and rattles after that install, hah hah! the speakers and most of the door panel hardware are now RTV'd in place.