Thanks for the replies, I ended up having to uninstall a terrible and dangerous installation from a Neon, and move it all into the Cougar.
I wish I had a digital camera; It was really unsafe. There were three "power" wires from the battery positive heading into the (absolutely disgustingly dirty) cabin; One was to the headunit, one was to the amp (all of like 14ga - and that was the big one) and one to god knows where.
The battery was almost completely green; I didn't want to break one of the battery poles, so I just pulled the fuse from the amp lead, and clipped and terminated the other two.
That thing was a mess. There was a ****ing gummi-worm, some half-full big-gulps, and; I'll spare you the details. It was gross.
The Cougar was the easiest install I've ever done. That rubber grommet (shaped like a teardrop, on the firewall straight back from the Airbox) is kick-***; they should have it on every car.
You could slide three 0-awg through there no problem, and still have room for three more 4-awg at the top of the teardrop.
Of course, the equipment was laughable; Two 12" DEI subs from the 90's, one with a damaged surround; And a Radioshack 200w amp. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
There was already a (JVC) headunit installed, so I just had to snap it out to run the RCA (that I'd salvaged from the other car), and splice a remote lead into the harness (no, not the factory harness.)
I ran all that on the passenger side, and ran the power wire through the aforementioned grommet, right down the driver's side, behind the interior trim in the back, and voila; Power to trunk.
Proud of myself, it went perfectly, I couldn't have asked for an easier job.
It even sounded pretty good, (read: not as shitty as I expected) and the owner is thrilled.
Made $40.