It looks like the tuner works. I took the wiring adapter, and spliced the yellow (+12V main) and blue (Amp Sense) lines together, so that the empeg would power the tuner. The tuner comes on and seems to work like a champ.

Any suggestions for a more permanent in-car wiring solution would be thoroughly appreciated.

Thanks to all who helped out in this thread and the other. Guess this is proof that the answers are out there, you just have to sit down and reason through it for a bit.