Those type rocker switches are prone to oxidation on the bare copper contacts and they don't self clean very well. I have had this problem (several times) and in most cases it took rocking the switch to clean a spot on the contacts.
No man has a good enough memory to be a successful liar. Abraham Lincoln
2016 36FBTS Pinnacle
2016 F350, 6.7, 4x4, DRW, long bed
B & W Companion 5th wheel Hitch