I'm in a somewhat similar situation and have ordered one of these from fleabay 301042038916
i'm not sure its the right thing but I can let you know - Again this is to earth through the body of the gauge hence just the one contact, If you have a similar gauge, you should be able to earth it as I will, the insert tube for the bulb is metal and already earthed.
I'm not sure what you mean by the "Charging light", do you mean the ignition light?
I am replacing a plastic two wire one as I am swapping out all my bulbs for LED.
If it works I could always send you the one I'm replacing the bulb is still fine!
Aidan