Wiring an AMC Machine Tach...Question...

I bought a Machine Scoop from an old guy and am going to install it on my 69 Buick SportWagon.....it has the factory pigtail coming out of it.....do you know what the different colors are for? There are 3 wires.....I assume the black is ground.....

Where would I hook the other two......to my coil negative side (green?) and the other to power (red?) in order for the light to work?

Thanks..

That'd b my guess, black-ground. red-switched 12V & that only leaves the green "sense" wire for the coil neg. does it have a light circuit, yellow??. But I would find out 4 sure as you dont want to fry it, might google it