Heh, I was about to ship out a retrofit kit.
A long shot of a reason could be the "cowl wire", a major wire harness in the car, has been replaced with one for cars without cruise.
I don't know if your car is manual or auto - you need to check into the engine wire harness for a brown-yellow wire from one of the 4 plugs into a junction connector buried inside the harness. It carries the torque converter lock-up signal and cruise brain needs it. If it is there, or yours is a manual, then just harness and switch. But you will either be looking at one of
1) the entire cowl wire, which requires removing the entire dashboard to get at;
2) major extrication work
3) bits and pieces with about 10" (wild guess) of wires from each key components. You get to supply wires and build up the rest. ie. lots of soldering.
I went the major extrication path, after extracting the entire cowl wire, because I pulled the kit from a junkyard 98 myself.