The connections I made were with wire nuts and electrical tape. Old skool I know, but I have done it this way since the '80s with nary a problem. In any event, I checked my connections so many times during the install trying to solve this I am pretty certain that is not the case.

A little more info - on very hot days here in NC, when the car has been outside in a parking lot and the temp is 94 or so like it is today, the Mode button works. If I drive home from work, eventually it cools down enough inside the car and it will stop working. This is repeatable behavior. I think there is a bad solder connection within the steering wheel interface. The power button never, ever works. I do think it's defective but I am not willing to rip it all out for the sake of one button that I actually care about (power button not important to me, the stereo is always on).

 

Well, there's three buttons per signal wire, so if up volume up and down both work, the wiring from the steering wheel controller is good. That narrows it down to the buttons on the steering wheel, the steering wheel control adapter, or the radio.