That kinda helps. I mean, it shows me what's what, but I can't understand how it works.

I'm looking for a conventional preamp/amp relationship here that I don't see. I see a radio, and I see two GND wires from that radio connecting to an amp, power to the amp, and speakers out from the amp.

I ...

Hiya,

I found this article here: https://www.matthewsvolvosite.com/forums/viewtopic.php?t=2557

It's good info for where the speaker wires are, but I'm actually looking to just replace my amp. Anyone have a wiring diagram for the line outs from the preamp to the amp? I'd like to keep the tape deck ...

There isn't a lot of room in the doors for deep speakers. You may have to choose thinner ones.