How daring are you?
The tach is usually dead as a door nail. If you can post a pic of that 4-gauge cluster, I can pretty much tell you if they work or not by their positions.
...If you want to, you can remove the tach from the housing. There is a long screw on the back of it that +12 volts connects to. You can clip a wire from the input of your ballast resistor to the screw. There is a lug on the back of the tach that needs to be connected to the "-" side of the coil. Other than that, you need to run a wire from one of the remaining three screws on the back of the tach, to some body ground...a valve cover bolt for instance. Seriously, if you don't know what I'm saying, don't try it!! Otherwise, you can rest this tach on your fender or on top of your cowl panel, and start the engine to see what you got.
