68 Mustang tach hookup
 

I'm trying to wire a stock Ford tachometer in a 1968 Mustang. I can't find the original connections in the wiring harness, so I'm running my own lines to the ignition and the coil (+). Does anyone know if I need to use a ballast resistor in the wire to the coil? I've read that you need to use one if your coil does not have internal resistance. My coil is a stock replacement from a parts store. I really have no idea if it has internal resistance or not.

Thanks.