Dimmer switch. Cheap, easy to change. Clean the socket contacts that it plugs into and put dielectric grease in there to protect it from corrosion. It sits in a bad place for moisture.
Craig

2014 Ram 1500 Laramie, 73 Cuda
Previous mopars: 62 Valiant, 65 Fury III, 68 Fury III, 72 Satellite, 74 Satellite, 89 Acclaim, 98 Caravan, 2003 Durango
Only previous Non-Mopar: Schwinn Tornado