Help on a 00 vert convert!! PLZ!

Hey all, I'm throwing in an amp and sub this weekend. I pulled out my back seat and the rear carpet in the trunk to expose the amps and wiring. Now which wire do I tap under my seats to splice the signal? My converter has two channels (right and left). Do I need both signals?

In order to get both signals, do I use the RIGHT and the LEFT amp? If you can help me, that would be great. THank you!

#1 What sound system came in your Mustang #2 Are you using the stock deck?

If its only one sub it ussually will only need to be wired in to one side. If you have two subs I would put them on dual channel, which will require left and right.