i dont know why all of those pins were unsoldered or if the cluster was the car's original or a replacement, or how likely this is to happen to others, but if youre starting to/have been having wonkey issues take the time to pop open the device because it may be something as simple as a broken or missing solder joint or that a 30 year old passive component finally had enough and popped. the couple hours it takes to investigate may make the difference between handfull of bills for a replacement assembly or pocket change for cheap resistors or capacitors or whatever.
i didnt take a before picture because i didnt think about it at the time but the pins on the left all the way up to the yellow residue is where the unsoldered pins were. that was the problem all along, no solder so no contact so no tach.
of course not all happy stories have happy endings. when i was putting it back together i decided to clean all of the plastic stuff with isopropyl alcohol and a microfiber rag to make it as clear as possible. not a big deal, until i used it on the plastic with the graphics printed on it... and it started wiping them off. ughhhhh. so there is your second protip of the day: dont use alcohol on silkscreened graphics!
