The piece that bolts on to the face should have a light bulb in it - take it off and have a look. A lot of old instruments used external lighting. That explains what that pair of wires is for.
The two wires coming out of the case would go to the meter + and - on the box. I would hook one wire up and just touch the other wire to the terminal (while engine running, of course)- if the needle moves backwards - reverse the connections.
