Standard trailer wiring would have clearance or marker lights on the same circuit regardless of the color of the lens. The running light circuit would be controlling them. Most likely the lights have a weak ground as you said they flickered and then stopped working. I'd check to make sure they are grounded to a clean metal surface. You should also note that a lot of trailer wiring grounds through mounting hardware so you'd need to make sure the mounting hardware is clean and free of rust/dirt.... view full answer...