Model 897 Dixco tach problem

[cwc]

My 69 nova has had this Dixco tach on the column for years,after getting it running again I hooked the tach up and nothing.it has 3 wires.green,red and black,red to hot,black to ground green to coil.i pulled it apart and found that the green wire has came loose from circuit board.Darell and I figured out where it goes, but it still doesn't work.strange thing to me is red only goes to light,there is a black jumper wire off lamp housing running to circuit board.does anyone have one of these tachs they would not care to pull cup off and see how it's wired?could it be possible that black goes to 12v