While the locations of the voltage regulators did vary over the years, I think there were only three or four actual positions. So if yours was farther forward, then I’m not sure what that hole is for either.
I also thought that was a picture of a hard top bolted to the body, but it didn’t look like any location I could think of.
In fact, it didn’t look like under the hood either until you mentioned it, because that hole back there looked like it was on a raised flange. And that did not compute in my brain!
Although, at one point in production, Broncos did have some voltage regulators bolted right over a similar hole. But closer to the battery I believe.
When I saw that, I always thought it was strange, letting water get in there.
So I just assumed it was for breathability and letting water get out. Which didn’t make sense either, since the standoffish nature of the mounting flange of the regulator would allow plenty of air circulation behind it.
I can’t wait to see a wider view so we can put it completely in context