This is how my dash looked a few days ago, after starting the car and leaving the key in the ON position several times. It also would randomly turn the headlights on and off no matter what setting they were on, and the power seemed to fluctuate as well (because the radio would flutter on and off), and a non-responsive tachometer. Then I went back to class before dealing with it any further, and when I came out it only had a check engine light on. I took it down to autozone to have the code read where the tech told me that they couldn't pull anything and sent me to a shop down the street. Unfortunately they had closed already for the day but the check engine light went away on the drive and all seemed good so I brought her home.
It drove around fine with absolutely no problems, sounded fine, all the electrical worked. Two nights later, I went out to check on things and it all seemed fine still. The next morning I came out and went to start it and it was 110% dead. No starter sound, no lights anywhere, couldnt even open a window or move the seats. She sat like that for a day because I was preoccupied with other work, and today I had a friend jump it. Took about 10-15 minutes for it to get enough of a charge to start. I left it running idle for a half an hour or so to try to bring the battery back up to some juice before leaving it overnight again.
But while it was idling, I noticed a few issues. The minor ones being that the compass was not reading the correct direction (and seemed to change randomly whenever the car was turned off/on), and the temperature reading 77 degrees while I'm in upstate NY with 28 degree weather currently... And then the major flaw being the tach bouncing between 0 and 1000rpm, without the engine changing speed at all (she was humming just fine at normal idle speed), and no tach reaction to touching the gas pedal (although the car would rev up as per usual). Also while just idling, the airbag light would periodically turn on/off, accompanied by a ding, or sometimes the ding but no warning lights, or sometimes all the warning lights, and sometimes the EVIC would say "check gauges, check transmission, check 4wd sys, etc.." basically every warning that it could.
Video of Tach Bouncing
Any help with even a remote idea of how to tackle this would be greatly appreciated.