[amagalla]

I wanted to chime in here because I've done the speaker upgrade process. I did't have the rears originally wired in, so I had no wires running back there. Because of that, I had to run my own wires to the rear. This is pretty easy and straight forward. I did have the factory "Hi-Fi" system (the hi-fi used here is subjective), so I had wires running to the dash and doors. With out this option, running wires to the dash would be easy. BUT, running wires to the doors would be much harder. All electrical connections to the door go through a harness on each door. You'd have to figure out a way to run the speaker wires through that harness. I've no idea how you'd do that.

One nice thing about the way the older Miatas were built is that all of them were wired for every option. Even if the feature wasn't there (power seats for example), the wires were. It cut down on the production costs as there was no need to build different harnesses for different cars.