No offense, but I'm very skeptical that the new deck caused the cruise control problem. BTW, do you mean the head unit in the dash or the CD unit in the trunk?
The wiring diagrams show an 88-92 system with Tempormat, whatever that is. On this system, check fuse numbers F1 (15 amp) and F17 (7.5 amp), both in the Front Power Distribution Box (i.e., Fuse Box) located in the engine compartment. Another cruise control system for 88-90 w/EML has no fuse at all but gets its power from a Junction Point. (FYI, there's a Rear Power Distribution Box located under the back seat for other stuff.)
If the fuses are OK, disconnect your new deck and go for a drive. Then, if the cruise control works again, then I can believe it. If it still doesn't work and if wires were spliced into, you'll need to then undo those as well and go for another test drive.