Oh hey. I got my laptop back from RMA (7 day turn around for dead motherboard, not bad at all) and was going to attempt to hack the connectors in my drive caddy. Turns out I didn't need to, it had an undocumented feature of a tiny switch at the back of the caddy which must disconnect the diagnostic pin from ground - and now my problem with sleep / shutdown is fixed! Thanks all for the comments, great help - for any future cases it's worth mentioning the teeny-tiny switch if people have similar caddies. Apologies for the crap photo, but you can see where I mean.