The license plate light is the farthest
12V electrical point from the TV connection. The tube is to drain off excess electricity after you disconnect from the TV to avoid electric shock or accidental spark. (Now, if you believe that - - - -). Kevin is, of course, correct. The original battery box had a lid with a vent that supposedly vented off battery gasses. Didn't work very well and PO's usually got rid of the box and the vent. You should provide some sort of vent for any battery except GMA or Gellcells which do not give off gasses as they charge. Darol