I have a 2002 Coleman sun valley and when battery is disconnected and running on shore power only, the over head lights do not work I checked fuses and circuit breakers all were good is my converter bad ?
Do you have a flip up sink in it? There is usually a kill switch that will keep the lights from working when it's flipped down.
Does the outdoor porch light work? That is my test light since it is not in the circuit with the kill switch or the canvas harness. But is still a 12 volt light.
On Colemans there are two connectors outside of the camper next to the canvas. I would check the one up on the roof line. Mine regularly comes undone and I have to climb up on a stool and reconnect it.
If your overhead lights work when you have a charged battery connected but don't when you disconnect the battery then your converter is most likely not outputting 12V. Confirm this by checking with an inexpensive voltmeter.
Yes that is exactly what it is for. It prevents the lights from being on when closed. That prevents the lights from setting the camper on fire.
Like SpeckHunter said if it works when battery is connected but not without the battery then it’s probably not the switch or connector. But I’d still check just for piece of mind.