Citroen Specials Club - the club for all lightweight cyclecars

With regard to the G S tacho-the 3 contact type, can anyone identify the 3 contacts.
Looking at the tacho from the back at 12oc there is the bulb holder, at 2oc there is a contact which I believe is the earth as this is fitted directly to the case and at 8oc and 10oc there are 2 terminals one I assume for the live feed and the other for the signal.
My problem being which one is which?
If anyone can throw any light on this I would be indebted.

Looking the back side, left and flat connector with white plastic around is positive.
Central bolted round connector with plastic around is signal and right is eart with a smaller bolted round connector.
I have 2 tachos on the table and both same connecting ...........
Thierry

if it helps I have the "hints and tips" paper on changing the GS tacho to run on 2 cylinders...email please... and will send.
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