if you have the wires cut, just ground the negative side of a speaker to the chassis, then balance your stereo to rear right and connect each wire one at a time to the positive terminal of the speaker until one wire make it play loudly. Then do the same for the other side. You can use a home speaker if you want since they are usually 6 or 8 ohm.
installing the amp in the trunk, the problem with popping off the back speakers is it looks like the whole back panel has to be taken off. BIG project. I don't think the speaker screen comes off on its own OR am I wrong?
oh and for line convertors or high level inputs usually just using the + signal is enough, if you use the negative side it could mess up your radio depending on its design.
usually back panels pop off pretty easily, I dont know on the mini but 99% of other cars do. Speakers are something that are replaced quite often so I imagine it cant be that big of an undertaking.
As far as taking rear panels off being easy, it is not like 99% of other vehicles, you do have to remove the seats to do so. Although its not hard, just time consuming, not even the techs enjoy doing that, fortunatly we seldomly replace the rear speakers, just a midrange in the doors from time to time. Again i wish i could be of more help supplying the correct wires, i just dont have the schematic available to release. Also there are many different wiring harness for different stereos, cd players, cassette players through out the years and would hate to lead you into the wrong direction.
As far as taking rear panels off being easy, it is not like 99% of other vehicles, you do have to remove the seats to do so. Although its not hard, just time consuming, not even the techs enjoy doing that, fortunatly we seldomly replace the rear speakers, just a midrange in the doors from time to time. Again i wish i could be of more help supplying the correct wires, i just dont have the schematic available to release. Also there are many different wiring harness for different stereos, cd players, cassette players through out the years and would hate to lead you into the wrong direction.
good info, if you need some help I may be able to lend a hand depending on where you live.