Need help identifying cartridge

[+x=usr(1536)]

For no very good reason at all, I decided to spend the evening digging through a bunch of 5200 stuff I received last year.  Most of it was pretty straightforward, but I did run across one thing I can't identify.  Please note that this is the machine upon which I am popping my 5200 cherry, so if I'm asking stupidly-obvious questions, please give me the usual ration

 

The cartridge has no label.  Inside, there's what looks like a 5200 cartridge PCB that someone's depopulated and repopulated with 28-pin sockets.

 

I have no idea where the grey wire should connect; it was detached when I opened up the cartridge.  If anyone has ideas on this, I'd love to hear them.

 

On the rear of the PCB, pretty much immediately to the right of the hole for the screw post, the text "CO18289 REV 7" is visible.  From what I've been able to sort-of figure out, that might mean that this was originally a Super Breakout PCB.

 

My money right now is on this being something that somebody was using to test ROMs that they had been burning, given that it looks like something I would have put together myself.

 

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