Tach does not work with new coil?

My coil in my 76 280z was looking pretty worn, and my car has not been running so well. I replaced the coil with an MSD Blaster 2HV and now the tach will work up to 1000rpm, then drop top 0 once it hits around there. It will move but it only looks like it shows about 1/10 what the actual reading is. I could tell the car ran much smoother at idle with the new coil though. Why would a new coil cause the tach not to work correctly? The car has a CraneXR3000 and no ballast resistor. I have searched but all the tach problems seem to be related to 240's.