Tach problems

I have a sunpro tach, when the engine is running, the tach needle keeps going up and down. Not sure why.. I have Mallory ignition box and ignition panel with push start.. Any thoughts?

My old Mallory Tach in my 69 it was loosing ground and the needle was jumping around would not do it until I got over 2000 rpm  I started checking all the connections when I found my problem check all your connections if everything good it more than likely the tach.