I can't tell what the light you mean is. One of my bays has a light just like an interior light. On mine, the lens slides out...sort of push down on it and out at the same time, sorta like a battery lid on the back of a TV remote control or cordless phone....
I had water coming in mine...not a lot, but enough.
Couldn't figure it out with certainty, till my daughter got in with a flashlight while I hosed from the outside. What she discovered was the cam locks they use on the doors are not weather proof ones. It leaks right through the tumbler...not the "gasket surface" where it's installed through the door, but right through the lock itself.
Just another thought... again not knowing what your rig is... my storage bays well two are different, but the others are nothing more than a box with one open side attached to the inside wall of the MH with a few screws and foam sealant. Certainly plausible that the crack staff at Thor might have missed a spot with the foam.