[Reanimotion]

the Opto circuit is for 0-12v only and will fry if connected to a CDI driven coil
the VR circuit is safe to 100v or so as the VR sensors normally generate fairly high voltages


I would try VR+ connected to pin 7 of the ignition control unit (the wire to the distributor)
that way you are sharing the signal direct from the distributor
and the signal is the correct type (VR) for both the CDI box and the MS
leave VR- disconnected

if that doesn't work for some reason then try VR+ on the tachometer(a) wire
leave VR- disconnected in this setup too

for the MTX-L chassis ground should be fine, although a shared ground would be better if you can manage it


The two shared ground wires in the MS should be connected to each other internally, use both if you can, and maybe extend one to the same chassis point you are using for the MTX-L