85 944 tachometer problem
 

85 944---My tachometer is reading very low rpm -it is starting at idle at 200 rpm and at what should be 5000 it reads 1000rpm. Problem -1st time since Ive owned it. Checked connection at the coil and I dont kow where the ground connection is?? Also could it be a fuse involved causing a weak connection?? If so which one??? Checked the manuals I have and no help.
Thank you in advance for your advise.