Tach problems

[still w.i.p '68]

I just put a tach in my truck, a mallory.
green wire to neg side hei.
red to switched power.
black ground.
white to lights
orange ? shift light-rev limiter?? not hooked up

any way I was givin this tach, without instuctions,
and this is typical wiring I think,
it doesn't work, Is there a way to test to see if its
any good, or have I done something wrong?
any help would be greatly appreciated....John