Had the same problem as you, only no lights of any kind. Slow down brakes would barely stop, checked all my grounds and connections, still won't work right, so I took my trailer to a shop that specializes with trailer brakes, axles, and electrical. Find out the last person that worked on my brakes four years prior, pumped to much grease in the fittings and blew out all four seals. Had to clean everything up. Thought I might have needed new brake shoes, but original ones still in good shape. Work good now, might want to look into that.
Larry and Wife Debbie
2016 Ford F250 Super Duty 6.2 Liter 3:73 Axle.
2004 Dutchmen Sport 26L 7546 lbs. Loaded.