Dad has an MD he started restoring a few years back but put it on the back burner for a while. He's back at it now and was wondering how the ignition is disabled when switching from gas to diesel. All he has is an I T manual which does not go into much detail. There is an insulated wire exiting the intake manifold that he thought somehow grounded out the ignition coil when it switches over. I doubt that would be the way it works with anything other than a magneto system (there's a distributor on this tractor). Any clue where this wire should be attached? It has a fairly large ring terminal on the loose end of it but I see nothing to indicate where it could have been attached. He's also wondering how to check the position of the intake butterflies since they are not visible unless you pull the manifold. Any suggestions from the experts? Thanks in advance.