Tach, speedo, volt meter, oil pressure jump around erratic and water temp gauge appears to be dead. Does this sound like a bad ground or something else? Thanks in advance.

had the same issue one time on a different boat, tried everything batteries , grounds,< finally replaced every large cable from batteries , switches, starters, grounds. then all was well, apparently one of them was bad but I did not check each on each one to find out which was bad, they were 10 years old and had some corrosion near ends