Following up from almost a year ago when I first attempted to hack (and broke) my Mint Plus, I've tried again! See?
Yeah, lots of wires, but sadly no real progress. I noticed on the board there was an RX and TX pair, so I traced it to where the battery port is. The battery connector has 5 pins, but the battery has only 3 (it's lithium-ion, so the third pin is for the battery IC), so the other two must be the RX-TX.
Hooking up to those pins didn't get me anything, but hooking up to the board got me a floating-high from the TX, although it never goes low. I've tried getting it into some sort of debug mode by pressing buttons and the sensors in various combinations, but no luck.
I can't continue anymore tonight as it's getting late and the Mint makes an obscenely loud noise on boot up that's getting on my nerves. Instead, I'll reassemble it and put it back on the charger for later use and hacking.
Back to work!