This morning (or was it yesterday?), while stripping the paneling off the rear interior, I noticed a harness termination on the driver's side E pilar that looked a whole lot like a ground point. It's right behind that side's rear speaker.
The BIG ground is off the engine bay fuse box.
Two to go...
I've got a pdf file of the workshop manual that probably includes the information you're looking for - but it's for a '95 V8 and TDI. I'll look at it more closely when I sober up a bit...