This is a constant brightness 3mm red LED arrangement that fits nicely into the hole behind the rear marker lens of the #963 observation car to give a bright, deep red end of train light. This unit maintains constant brightness from 6 to 20 volts AC or DC. Simply solder wires from the legs of the unit to the truck rivets and tape or hot glue the unit into place. It stays constant on with AC power but is only on in one direction with DC.