Stewart Warner Tach wiring

[JKZ27]

Does anyone have a wiring diagram or installation instructions for an old SW 960AA green line tach? I've got one that I'd like to install but I'm unsure of the connections or if it requires a sending unit. It has 4 unlabeled studs on the back and I'm pretty sure 2 of them are just for the the mounting bracket. Any thoughts or suggestions are appreciated. Thanks.

John