I drive a Demon (and not the other way around)

Carpet was going in, suddenly, the horn began to blow. Got out of car to disconnect battery, closed door horn quit. Opened door horn sounded. Very strange. This happened about a week ago. I began chasing circuits with a wiring diagram. As I got under the dash, I was surprised to find a bunch of wires had been cut for the installation of a non-factory cruise control that look like a factory job and the installation of an aftermarket radio (8-track in-dash). Have to replace the wires. Repair not feasible. Dilemma: Do I try a factory-like dash harness or do I go with a Painless tip to toe deal? Does the Painless system have provisions for the NY state required rear defroster. (REAR AIR in Mopar-speak)? grumble, grumble, razzlefratz.