In that shot, it looks more like a protruding reddish cylindrical shape, probably identical to the circular reddish feature in the bottom right corner of that photo. If you look at the top of the shape, it's flat, like a hockey-puck shape seen a bit from the side. Although I will admit that there's no hint of such protrusion in the overhead angle you posted.
But if it is just like that forward feature, then I guess it isn't a switch, just a slightly protruding light fixture.
As discussed a couple of times before, it seems that Kirk steers deliberately into that storm, having every opportunity to fly in other directions at high speed yet still opting to approach the storm at a steady warp one. The role of the ion pod might not be to protect the ship from the storm, then, but to gather crucial scientific information Starfleet wants on ion storms
That's a given. It's explicitly stated in the bridge log tapes in the episode: "We'll need somebody in the pod for readings." Spock then orders Finney to "Report to pod for readings on ion slates" (or so says the closed captioning -- some people in this thread have said "plates," suggesting something analogous to photographic plates for X-ray instruments, say), and Finney later reports "Ion readings in progress." The ion pod was quite clearly depicted as a scientific instrument.
I imagine the pod might be something that extends a telescoping antenna/probe out into the storm, kind of like a lightning rod. The pod and its extended probe are insulated from the body of the ship proper, but an intense enough charge can jump the gap, so the pod must be jettisoned if the storm's energies grow too intense (since it might not be possible to discharge the pod safely past that point).
- so badly in fact that it tells its captains to deliberately fly into storms at the risk of damage or casualties.
I guess that depends on how big the storm is and how feasible it would be to fly around it. Although I assume that an ion storm is typically a coronal mass ejection from a star (I've even seen the term used that way by scientists at least once), it's possible that some ion storms are larger, similar phenomena, maybe interstellar plasma clouds energized by distant gamma-ray bursts. I'm fairly sure there are episodes referring to ion storms that are too big to steer around.
If, OTOH, the pod is just a contingency measure, Finney's master plan becomes impracticable, as it might never happen that a storm and Finney's shift would coincide. Finney should then be considering other, less impractical ways to frame Kirk for murder, in which case it makes little sense that he would not already have tried a trick or two during his long years of harboring hatred.
Who says he had a master plan? I've always seen it as an extemporaneous decision. His hatred for Kirk had been festering, and when he happened to get the ion pod assignment during an intense storm, it suddenly occurred to him that if the pod were to be jettisoned, he could jump out just before and hide in Engineering, and people would think he'd died. Then he'd simply have to get to a computer terminal, do a little video editing on the bridge records (easy for a records officer), and bingo, Kirk's framed for his murder.