Do you mean only the trailer stop lights are not working?
Are the brake lights on vehicle body working correctly?
The CHMSL fuse (10A) is for the brake lights. If battery voltage is not available athe trailer connector, check the CHMSL fuse. Use a test lamp to test both ends of the fuse. If voltage is available and none found at trailer connector (Light Blue wire), you have an open circuit between the fuse and trailer connector.
Wednesday, January 12th, 2011 AT 2:39 PM