The vast majority of automotive electrical problems are poor or broken ground. I would first test the bulb, then the socket for the presence of 12V, corrosion in socket, or bulb contacts. ie: what Rooster said.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"