I recently put a tach in so maybe I can help...

the red wire is power... you can hook this to any constant 12v source. This is when a voltage meter comes in handy. You are on your own with this one... but yes you can hook it to an ignition switch power wire.

the Green signal wire.. you can hook this to the coil. From what I've read it is a thick blue wire with a white stripe. What i did though is splice the tach signal wire going into the dash pod... it was a small blue wire with white dots on the stock tach side.

the white 12v Light wire gets hooked to a light source that turns on with the parking/headlights. you can splice into the stock dimmer switch for this...

I hope some of that helped.... it's late I'm tired.