Tachometer picture/wiring question

[X33RS]

Going through my stash and have this tach in a box.   I'd like to temporarily run wires to it from a running car just to check and make sure it still works.  My problem is that most factory tachs I deal with have "GRD" or "+" "-"

This tach has none of that.   Could someone possibly tell me from this picture which is key on and which is coil??  I don't want to fry this thing accidently.  Thanks

[X33RS]

Either I'm good at stumping you guys or this is just too easy 

I decided to take a chance and temporarily wire it on a running car with a correct working tach.  I figured if I fried it I'd just buy another one.  So here is what I found, maybe this will help someone.

As pictured above...
Top right goes to coil
Top left goes to key on power
Bottom is ground.

Interestingly, when you switch the top two terminals the tach still functions but it reads almost exactly 200 rpm slow.   Hope this helps..