engine analyzer questions

[mrlaser]

I have an old Craftsman engine analyzer that is for 12 volt systems. I am wondering whether this can be used on a positive ground 6 volt system if a separate 12 volt battery is used to power it? I am particularly concerned whether the pictured connection to the coil can be made. Any help would be appreciated. This was a very common testing instrument, so I am hoping that someone might have already have had this issue.