Testing security light socket
I have a dusk to dawn light that's not working and tried to test the socket. Covered the sensor. Used a multimeter. When I put the black on the center and the red probe on the socket threaded part, the digital numbers on the meter jumped around like crazy. When I switched the probes (red on center and black on threaded part) same thing happened.
First, which is ground on a socket and which is hot?
Second, why are the numbers jumping all over the place?
I tested the multimeter by putting the red in a receptacle slot and the black in the ground prong hole and it read 124.5 so I'm guessing the meter is working correctly.
Any help appreciated.