Switch on, both hot and neutral reads 120 disconnected and separated at the ceiling. Switch off, the neutral reads 120 but the hot reads zero.

I’m thinking I do need the vents. I live in a desert where the UV heats the interior of the container significantly. (Above 130f).

I’ll be storing electronics and furniture in there and don’t want them subjected to moisture or high heat.

The exterior plywood is a good idea. Kind of like making a miniature roof for the roof of the container?

That absolutely should not be happening. Separate and test both neutrals at the switch box.

If you have locking needle-nose pliers, you might be able to get a good bite. Lock it tight and slowly rotate counterclockwise.

If that doesn't work you could try the dremel tool method to cut a flathead screwdriver slit.

This side is correct then.

With the switch on both blacks show voltage. The the switch off, only the one shows 120 as the other shows 0.

Take the lamp out, and with the switch on, check if the socket has power. If you read 120v at the socket, it's the lamp. Or the metal plate at the bottom of the fixture isn't making contact with the lamp.

At the light the neutral shows 120 with the switch off which I'm pretty sure isn't supposed to happen. I haven't checked the connected neutral wires at the box since it's capped off.

Then your ground is properly connected and your neutral is not neutral or does not make it back to the panel.

At the switch, do you have one black that is showing voltage and one that is not, and are the neutrals showing correctly?

Then at the light, with the switch off, are both showing 0?

Is it a tub with a shower or just a tub? I’m wonderful you accidentally bent the actuator to turn the shower on and it’s partially stuck between tub and shower mode? If that’s not it is there an old linkage with a lever somewhere that used to activate the drain stopper?

If you haven’t flushed the water heater in several years probably better to just leave it as is. Some risk

The black to ground and red to the hot wire then to the neutral wire.

😏 never turned them off but thanks for checking. I know sometimes that can be a "oh yeah!!!" Moment

https://imgur.com/a/kNP90sA

Here are pictures and some explanation. https://imgur.com/a/kNP90sA

Here it is in detail and separated. https://imgur.com/a/kNP90sA

Buy disposable brushes at HD or Lowe’s. Put on multiple coats to ensure coverage. Wrap in plastic between coats

I will. I thought that was odd as well

Not to ask the dumb question first and be that guy, but did you turn back on the valves at the tub?

Why is your neutral reading 120? There should be no voltage on your neutral unless its part of a closed circuit. Are you sure your wires? Older houses did not pull neutrals to switches and often used a white wire in the pair as a switched or hot leg. You may want to post a couple pictures.

I purchased another fixture and light switch earlier today so I don't think that's the issue. Should the neutral at the fixture be reading 120 with the switch flipped to off?

Damp is fine. For future use, get a brush & roller spinner. They're like $10 at the local big box stores. They spin your brush real fast and it ends up damn near dry.

Where did you put your two probes to measure 120v on each wire?

Ok with switch in off position and wires not connected to fixture: The neutral reads 120v and the hot zero. With it in the on position both read 120v. That's the light fixture.

The hot wire from the source always reads 120v regardless. The wire at the switch going to the fixture reads zero when the switch is turned off and 120 when on. The neutral wires are capped and the grounds are spliced with a pigtail to the green screw.

That's correct. The drain grate/insert was replaced and bam. No pressure. I know it should not affect the drainage and feed, which is odd.

Both hot and cold are low, but only in the bath tub itself. The bathroom faucet is just fine, as well as the toilet.

We are on well water and the well pump was just replaced this past week ( the coupling was busted ).

I have not flushed the water heater. How does one do that?