So your sill lights did work normal when new?


First you need to be sure you are getting the 12v to the inverter for the same period of time that the dome light is on. If so, unplug only one sill at a time and try again. You could have one light panel failing (pulling too much current) causing the inverter to time-out or overload. I am not familiar enough with this type of lighting to properly diagnose beyond that.


James