Zenith T-O 3000 wall-wart question

[Jeffhs]

I have a Zenith Trans-Oceanic 3000-1 all-band radio, an eBay score about a year and a half ago. It works well, but I am wondering whether this radio uses a positive- or negative-ground wall-wart; that is, is the tip of the plug at the end of the cable positive or negative? (This question was answered in another post, but I haven't found it yet.) I would like to wire the wall wart permanently to the radio, as I don't carry it around at all (too heavy). I wonder about the ground on the wall wart because of something I read here in VK some time ago, that if the wall-wart plug is wired backwards, it can destroy the audio output transformer and the output transistors. This radio sounds great on FM, so I don't want to put it completely out of commission.

Also, I am wondering about a loose wire I found on the battery case. The schematic shows it as being connected to the negative battery terminal, but the battery case in my set does not have such a terminal (this radio was modified by its previous owner to use a rechargeable NiCad battery pack, so the battery box is not original; there is also a battery fuse in series with the positive lead to the pack). If need be, I will use the battery box from my Zenith T/O 1000-1, but if the 3000's can be rewired I'd just as soon use it.

Thanks for any and all replies.