I'd first check the bulb in the non-working light.  If the bulb is good – check to make sure you have 12volts at the connection.  If you have 12 volts then it is a bad ground.  A ground problem can be the most difficult to find.  If you have a ground wire at the connector check it connection at each end.  If there is no wire it can be a bad connection between the bulb and the fixture, or the fixture's adjustable mount, or between the mount and the bumper.  Invest in a 12 volt tester (It looks like a ice pick or screwdriver with a wire coming out of the handle).   It is the best tool for troubleshooting lighting problems – a digital voltmeter is to sensitive and will lead you in the wrong direction.   I can help you out at the meeting next Saturday if you are going…

Jeff

Cool see  you then.