TeamSwift

Hey everyone, I recently purchased a 93 Swift GT and have been fixing little things here and there. One thing that has me stumped though is the tach. It does work but barley. At idle it sits basically at 0 and know matter how high I rev it, it will only ever go up to 1000 rpms. Crusing at 55-60 it will maybe read 500 rpms. I was thinking it could maybe be a ground but everything else in the dash works perfect speedo, fuel gauge, temp gauge, and lights. Car had been sitting for sometime before I got it, any ideas what it could be?