It is hard to see oxide thick enough to stop 12 volts. But that is what it has been every time one of my front corner lights quits working. Every time.

One has to get used to the idea a multimeter does not work to verify power if you stick the probe into the end of a wire with the load disconnected. You have to probe the circuit with the light bulb in place -- then chase it to where the voltage is missing -- or possibly present on the ground side. When that's not convenient use a test light with a real light bulb in it. (Not an LED)
--
Art Benstein near Baltimore

A nun, badly needing to use the rest-room, walked into a local Hooters. The place was hopping with music and loud conversation and every once in a while "the lights would turn off." Each time the lights would go out, the place would erupt into cheers. However, when the revelers saw the nun, the room went dead silent.

She walked up to the bartender, and asked, "May I please use the rest-room ?"

The bartender replied, "OK, but I should warn you that there is a statue of a naked man in there wearing only a fig leaf."

"Well, in that case, I'll just look the other way," said the nun.

So the bartender showed the nun to the back of the restaurant.

After a few minutes, she came back out, and the whole place stopped just long enough to give the nun a loud round of applause.

She went to the bartender and said, "Sir, I don't understand. Why did they applaud for me just because I went to the rest-room?"

"Well, now they know you're one of us," said the bartender, "Would you like a drink?"

"No thank you, but, I still don't understand," said the puzzled nun.

"You see," laughed the bartender, "every time someone lifts the fig leaf on that statue, the lights go out." "Now, how about that drink?"