tach not working

Question:
My car 1970 Duster 340. A while ago the engine would not start-no spark and after much investigation, removing the tach feed wire from the neg side of the ign coil, the engine would start & run. Fast forward to now-after getting the instrument cluster rebuilt incl tach the engine still wont start with the tach feed wire attached to the ign coil. When you remove the wire, it starts like before
Any ideas?