'65 Tach Testing

[Rickmustang]

I have an original 1965 tach that I want to test before I reinstall it in my car as I'm not sure it works. What's the easiest way....hook up the coil wire and a positive wire, along with grounding the case, and starting car? Do I need all three hookups (coil, +, and ground) or can I just do a subset of those. Thanks.