Hmm, I did push it briefly (with the third port) and didn't even think to check the horn switch. I figured "the horn ain't there, the switch don't matter". I look now and the switch is "On". I'm glad the horn wires were not dangling and making contact inside. Well, nothing blew up, so I assume they were not touching.
I have a replacement horn ordered already, should be here by Dec 1 (and handle by Dec 4). I'm going to have to find something to cover the hole temporarily while I check it out at a rehearsal tonight (one of my practice amps is there already to compare to - a Hartke ha500 sitting on an old Peavey 2x15). I already know tone is better, but volume will not quite match - but I want to see how close it gets

May have to resort to duct tape. Yes, I have goo gone ready at the mere mention of duct tape, heh heh.
(The Hartke is nice, but there's just something I can't tweak out of it around the low-mid range on any cab I plug it into - maybe around 100-150 Hz. I don't notice it until about the third time I use it on any cab. Not muddy, not boomy, some sort of weird mush not quite all the way to the bottom. Used it for many years as a main stage amp, but now its bugging me)
I don't know if the 500 was owned by the same person as the 200, or if it is complete coincidence that they were in the pawn shop together. I've checked out the 500, opened cover (horn there) and played a guitar through it to verify all knobs and buttons work as expected. It is in very good condition, and could have come off a GC floor. No tolex issues, grill is nice. Like new.
Wait - I said off a GC floor - I meant appearance, not functional aspects... Okay... no, maybe a box from the back of GC.. uh... hmm, not a GC at all, but received new from an online order. Yeah, that's it. That's what I meant to say, newly ordered.