Tim
On a modern tach there should be four wires:
Ground, perhaps the case, perhaps a green or black wire. This should go to the chassis of your negative ground car
Power or +12, perhaps red. This should go to any convenient switched power source. Switched sources are often white or green wires in the bugeye. Green are fused, white are not fused
Sense, who knows what color. This should go to the "Points" side of the coil. If your coil was properly reversed when the electrical system was changed, this will be the negative side of the coil.
Lighting, again who knows what color, but is the power for the light inside the tach. If you can find a red wire with a white tracer or band on the bugeye attach the light wire there and the tach will light when you turn on the dash lights.
Disclaimer: I have never seen your bugeye, please verify your wiring matches my suggestions.
Cheers, good luck