Guys, honestly the number of times this is debated!!

It makes no difference (to the MSD) whether you leave the ballast resistor in or not. Yes originally it is there to step down voltage after cranking, but the MSD supplies the coil +ve via the orange wire and earths through the black wire to the coil -ve. The small red wire just needs an ignition-switched source, it doesn't feed the coil at all. MSD often show that switched source as the original coil +ve feed wire - it's just a handy switched source, that's all. The MSD unit can live with that being 12V or less (i.e. via the ballast resistor). It does not affect the output, the coil etc.