First verify the unit under the hood is pluged in. Also that the cable to the TB isnt broken. From there It may be a fuse. Or bad switches on the column. Or bad drop swicth on the end of the master cylinder.
Worst would be a wiring problem. Or the unit is bad.
I had the same issue on my Gen 1. I removed the pressure switch and applied very, very slight pedal pressure only enough to release a bit of fluid AND an air bubble. Re-installed the switch and it worked perfectly since.
I had the same problem after a winter of not using the cruise very much. I was about to try a lot of the suggestions here, but it turned out to just be a dirty or maybe corroded switch. After a bunch of times pressing it, it started working fine again. Was still working ok when I sold it a year later.
I have had this problem for a while, and hadn't been on here in ages. I am so glad someone answered this along with the Amazon link. I was able to order the part and replaced it yesterday. Now my cruise is working again, just in time for a multi-hour trip this weekend. THANKS