It is very likely to be the connector either end. A bad or oxidized contact leads to a higher resistance obstructing the free flow of electricity which gets converted to heat(whatch this one - can be dangerous by starting eventualy cable fires). Little or no electricity reaches your OBC. You will find reduced voltage in the OBC. While the electronics just don't work under a certain voltage level your lights inside(because of their simple electronic design) still work. Like a torch with old batteries. Maybe your OBC lights are sometimes brighter than other times. This would be an added indication for a bad contact somewhere. Hope you find it. Best Regards Ralf