The Insight now has a newly installed cruise control system, which works great! ivo, decibel45, and bovineone came over on friday evening to start the install. We installed the throttle adapter, built a bracket for the main cruise control unit in the engine compartment, ran the wiring harness through the firewall, connected the VSS (vehicle speed sensor) signal to the engine computer under the passenger footwell, installed a disconnect switch on the clutch pedal, and finally realized that we didn't quite have enough wire connectors to do the final bit of wiring.
In between there, Amy made us all a great fajita dinner, which was just the thing we needed to get as far as we got. Thank you Amy!
ivo came by the next morning with a wire connector kit borrowed from bovineone. We finished the wiring, visually checked everything, and took it out for a spin. We got no action on the cruise control system at all.
We came back home and started on the diagnostic routine. There's a small diagnostic LED on the circuit board of the main control unit, but it wasn't lighting up at all like it was supposed to. We figured we might have an electrical power problem. I didn't have a multimeter, so we made a quick trip to Lowe's and picked one up. Almost immediately we found the problem: the ground connection for the RF receiver module was not really ground. We fixed that, and the diagnostics routine worked perfectly.
We took it out for another test run, and it worked exactly as expected. All that was left was to tidy up all the wiring. The buttons on the steering wheel are a small wireless transmitter, which is the reason for the RF receiver module above. It just clips onto the steering wheel and looks just like it was designed for the car.
The whole project probably took 7 or 8 hours total. That's about the same time that another Insight owner took to install his cruise control the first time. Like him, we could probably do it in less than half the time now that we've done it once.
Thanks to everybody who helped. This is going to make our upcoming 5000 mile road trip a lot nicer.