Low fuel warning light

[Rob knights1967]

Hi there 

I own a 1986 Vauxhall Carlton 2.2GLi petrol, It’s the last of the mk2 before the more rounded model. 
I can remember when I had my first one  tgat was also petrol that I bought the circuit board and a garage wired it so the low fuel light would work. 
I now want to do the same again. I have the circuit board that slips behind the fuel gauge but am unsure how to wire it in. 
the board has 4 pins attached to it and looking at the circuit diagram there’s one wire that goes from one side of the fuel gauge and the other wire to the other side of the fuel gauge. I would imagine that the other 2 pins are for the light. 
can somebody please help me out with the wiring

  Tia. 

[Vauxhall Owners Club]

sorry but can't find anything on the net, found the circuit boards for sale in Germany on eBay but that is about it

Obviously, being sensitive electronics you wouldn't want to reverse connect any terminals so maybe an electronics expert can tell you which one is likely to do what and then go from there