So I told you guys I'd do a How-To on this one and here it is!
So first off, I have a factory Bose system in my '01 Roadster so that changes a few things from the other tut's I've seen online so far.
I am not an expert.
I am fairly handy and somewhat familiar with working on electrical systems in cars, but my car audio installer buddy provided a lot of help and guidance throughout this process as well. If you're not familiar with these systems or how to do anything I've mentioned below, it may be best to keep doing your research or find some helpful friends. This info is provided to give others a good idea of what they're getting into and just one way to go about installing a sub in this vehicle.
This first picture is of the passenger side of the car in the rear. To get the panel off you have to remove the bronze/gold colored bolt that holds the seat belt there with a 17mm socket or wrench. To get to it you just pop off the cover that's there. Next, what I did was proceed to just pull off the little rings around the roll bars and scoot them up the roll bar a bit. Then you can just pull up the top panel part, it's just pins holding it. Next I went from the outer edge to the center edge when pulling the main panel off. Once again just pins holding it there. The center edge of the panel is just under the center piece where the sub is so I just popped the last pins and slid it out a bit! This step (removing the main passenger panel) is not 100% necessary but I found it useful for putting the power cord through to the trunk and also for more light while I was inside the trunk on the other side. More on that later! :P
Here's a closeup of the Bose amp. Nicely hidden behind the passenger, rear speaker. Not easy to access anywhere except the trunk. Which you must get into do anything... a flashlight helps. I had a shop light, luckily. The Blue-Green and Green-Blue wires at the top are the speaker wires for the sub, which I spliced my RCA line out converter into. Just merely twisted the positive L & R and negative L & R wires for the RCA line out converter together and soldered them to the stock subs wires then taped it up after zip tying the new wires to the old to prevent damage from tension. I will have to check which is positive and which is negative again and I will edit this post once I get some light to check for everyone. I am almost certain Blue /w Green stripe is the negative wire. You can always use a multi-meter to find out as well. So once the RCA line out converter is on there you can plug in your RCA plugs from whatever wiring kit you got and that's all set to go!
This is a pic of the amp from outside the car for a better view of where exactly it is. To get to it all you have to do is pop put the two pins holding in the middle cubby hole and remove the floor mat and the cubby.
This last picture is of the sub wires that I spliced into. They run clear across to the sub from the amp so they are very easy to splice into!
As for the power cable, there are posts both here and on Waks Wide Web
detailing how to get it through the firewall. (Keep in mind the Waks Wide Web page is about a UK TT. The Glovebox is on OUR driver's side.) It's just as easy to remove the dash panel though.
The easiest way to do it is take a wire hanger and stick it thru from under the driver's side where you see the wires coming in. It's right above the kick plate but behind the rubber guard so you just have to bend it back to get access. The cables come through the firewall right UNDER the wire loom that the website I linked describes. So when you stick the hanger through try to poke the air box and then just go to the air box and pull it up and tape your wire on there! From there it's pretty self-explanatory as far as routing your cable from the front to the back. I used a plastic shim to get the wire under the panels all the way back and it worked wonderfully. Since I already had the passenger rear panel off I just tossed the wire into the trunk from there. For the ground I used a wire brush to remove some paint that doesn't show when the cubby is on and some self-tapping screws to secure it.
Now is when I forget which wire is the one I tapped the remote into so I will have to get back to you guys. I just used a multi-meter again so I didn't commit the wires to memory, unfortunately.
And from there it's gravy! I hope everyone enjoys the How-To!