Urgent: Do you know about installing gauges?
 

My car is in at a garage at the moment. They are trying to wire up an electrical oil pressure gauge (Autogauge) for me, but I have no instructions.

There are 3 connections on the back of the gauge labelled "S", "G" and "I". Can anyone tell me what should be connected to each, because they're stuck without the info. :(

Really appreciate the help.

David