Maybe the top light is burned out....it happens.
And yes, Walmart carries Multimeters. Just go over to the automotive and look in the electrical area (bulbs, fuses, wires, ect. Even the very cheapest model is better than none at all. Basically all you need is one that will measure DC and AC voltage and resistance (ohms)...that will tell you if a wire is connected or disconnected, like broken or such. Also good for testing grounds which is very important.
Be sure you have a multi-stage converter. Leaving your rv plugged into shore power with a single stage converter will destroy the battery by over charging.
Good luck
Ron
