"Seem Clean" is not good enough, you need to take them apart and clean them to make sure they are clean, first rule of electrical troubleshooting is to make sure the electric has the cleanest path possible and that takes more than looking at them. I spent to much time in the RV business helping my buddy out who owns a manufacturing facility to depend on "seems clean" do it the right way and you will track down the problem.
I am going to bet the contacts in the light switch are dirty and interfering with the electrical path.
Many of you guys don't remember growing up in the day and age when you are driving down the freeway at 60 mph and you hit the switch on the floor to dim or brighten the lights and all of a sudden you didn't have any lights, dirty dimmer switches were a pain in the you know what!
:faint2: