I will assume that the 1500 tach is an inductive tach like the 1275 tachs are.
If my assumption is correct, then all you have to do it put it in series with the positive lead to your coil and supply 12 volts to the 12 volt terminal and hook up a ground wire to the case. Start engine, marvel at you brilliance. The connectors for the unductive coil are the two bullet connectors. One is male, the other female. Now, I am not sure is direction of current will affect the tach. If so, just reverse them if the tach does not work initially. Anyways, the spade lug on the brownish PC board is for the 12 volts and a ground wire can be attached to any convenient bare metal part of the case but there should be another spade lug back there.
Hooking up stuff like this is easy for me but can be confusing for some folks. If I can see the circuit in my mind I can build it with test leads. I have built entire vacuum tube guitar amp circuits with test leads just to prove an idea.