Just to end the post string, I was able to tap into the tach wire at the back of the tach, but if you ever have to do it this way it's literally a pain in the neck and back to get there. Used long needle nose pliers to disconnect and connect the connector.
By the way it was a little easier if you take the light bulb connection out of the socket at the bottom of the tach gauge. That way the pliers will fit fairly straight up to the connection.
Lesson learned.
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