MOPAR Performance Ignition "MSD" tach Qustion...

A quick qustion in regards to the Mopar Performance digital ignition system PN#4876728 (MSD 6AL) and the use of a vintage Sun Super tach. I have the original wiring diagram that came with the tach. The MSD ignition has the provision for a tach hook-up on the side. Has anyone here used a vintage tach with this ignition? The instalation instructions say the tach output on the controler produces a "12volt square wave signal" is the same signal as the use of "old school negitive side of the coil"? Any help would be greatly appreciated!

Woodie.