I have a 2017 1500 Big Horn and the interior lights used to come on when the doors were opened but have now quit. They still come on sometimes when I hit unlock, they still power on with the door opened and I manually turn them on (with the truck off), and once I get inside and turn the key they come on for a few seconds before fading out like they normally would when opening the door and then closing it. It was a sporadic thing but now it seems like they never come on when I open the door. The dimmer switch is not turned down and the battery was recently replaced (problem happened both before and after the replacement), so I don't know what else to check.

 

If you leave your headlights on, remove your key, and open the door does the chime come on warning you that the keys are still in the ignition? If not, the door pin switch internal to the door latch mechanism is probably failing. Sometimes spraying some electrical contact cleaner into the door latch can get the switch working again for a short time, at least long enough to help convince you that's the issue.

I haven't had a reason (fortunately) to pull a latch from my Ram yet to learn if the microswitch is internal to the latch or accessible without drilling out rivets. If easily accessible, a new switch could likely be sourced for MUCH less than the cost of a new latch mechanism.

-Rod