Just a word from experience,CHECK THE 4-PIN TRAILER CONNECTOR FOR CORROSION... Should this aux. connector become inverted with the connector pointing downward the cap will fill with water/salt/sand and other conductible stuff and start to draw current from pin to pin. This may cause erroneous code or lamp related diagnostics ! Found mine to be a green / crusty mess. I had to clean it out with a . 177 caliber rifle brass (brass) and lube it (pack it) with silicone grease.
Mark T.
Mark T.