I too was amazed that they don't cause an explosion. The explanation of not enough oxygen is one thing but there are occasions where trucks sit with little gas and people try to start them. Obviously it works or there would have been many incidents over the years.
The Gauge: If you can't get full movement while it is mounted in the truck with open and short circuits on the sender connection, then you have a connection problem. The gauge needs to be well grounded in the dash.
