Hardwired stereo?!

The Imperial's deck functions...kind of. It has an issue shifting the audio properly through the speakers via the volume knob. So I picked up an equalizer-equipped deck from an '89 Fifth Avenue. Figured it'd be a cakewalk swap.

Bad enough that both the Fifth and the Imperial have Chrysler's "bastard bolt" security screws. But once I got the Imperial's deck loose, I find that there are no "plugs" for the wiring, but that it goes straight into the deck casing. Looking at the schematics in the electrical book doesn't really help me...anyone dealt with this?
Author: Bryan M.