1966 TrueSpeed Tach.... Where to get info?

[Mark42]

I removed the Truespeed tach from the dash of my boat and found that it looks to have never been connected. The screw terminals show no screwdriver marks, and there were no wires connected to them, or any under the dash going to it. The lightbulb looks brand new. I noticed that when the tach is slowly shaken the needle moves in its arc nice and smoothly.<br /><br />I want to test it, but have no idea what the connections are. It is has a square chrome housing with 0-7000 or 8000 rpm sweep that is almost horizontal. Two screw connectors on back. Has a date of 1966 on a tag. <br /><br />Know where to get info on this tach or what the connections are? I searched the web with no luck.<br /><br />Thanks,<br /><br />Mark.