Tach wiring revised

[RAY WYGONIK <RWYGONIK@grove.iup.edu>]

I forgot to mention the car is a 74 MGB.  The ground terminal is a spade
terminal along with the terminal for the green wire.  The two other terminals
are plug terminals.  A white/black wire with a female plug terminal is hanging
out of the wiring harness in the area of the tach and I can't trace it to
anything else.  I have a female plug terminal on the tach with no apparent
match.  The light is accounted for.  Question is what color wire to this extra
terminal or it's origin or is it even necessary?