Wow, sounds like you've tired a lot so my suggestion may be a longshot. After getting caught in a big rainstorm, the tach itself showed comdensation behind the lens amd my digital display (in the tach) started intermittently showing "NO DATA." Soon thereafter, it went blank and then my gauges stopped working entirely. I disconnected just this gauge and then all others started working again. Plugged it back in and the rest stopped working.
One other thing I stumbled upon purely by accident was that when I pressed and held the Display Selector rocker switch in the down position, the entire gauge set seemed to run through some kind of self diagnostic routine. First they all rotated in unison to 1/2 way point, paused, then to full point, back to zero, half, full and back. Looked kind of cool!
"This one goes to eleven." 2007 ProStar 197 TT w/MCX and Powerslot.