Ok that is the power supply for the booster (Which is in the antenna) Now, we get to tribble slaying.
Turn the light OFF
Go up topside and disconnect the coax from the antenna head
BEING VERY CAREFUL TO NOT SHORT the center wire to the shell hook up a test lamp.. This is a ice pick like thing you find at Auto Parts stores or departments, Insulate the clip and clip it to the center wire, make sure it metal of the clip does not touch the nut.
Turn on sight
Touch tip of probe to the metal "Shell" Bright light good, anything else bad.
Next step after that..
If good. turn off the light, and re-connect
NOTE: ONly connect, disconnect, light off.
Next step
The cable from the antenna goes only as far as the roof. Either sticking up through the roof buried in Dicor caulk or burried under a "Clamshell" cover that is covered in caulk is a connector.. Test here, use new coax
On my Antenna when it quit working this connector was..... Toast
I replaced the connector and a cable end or two and ... Studio quality.