tach for mag ignition

[corvair kid]

I have an old Bendix tach for a mag ignition and I was wondering if it would work on a 1960 40hp Johnson. It has 2 wires on the back one of which says mag. The other says nothing. It also has what seems to be a place for a c cell battery. Any input about how this thing hooks up and the deal with the battery will be greatly appreciated!