Any joy?
Some cars have a 'fusible link' (piece of fuse wire) buried in the harness as an uber-fuse - should only go if something drastic like a shorting starter or other MAJOR dead short to eath happens. Pretty sure Beezer just has whacking big blade fuse for that tho.
Working through it, -ve terminal to chassis earth; +ve terminal to starter>alternator>main feed to fuse box bus bars>rest of car.
Pretty sure radio circuit shouldn't be live unless ignition is live.
To be honest, it's time to get a meter out and see what's where relative to what.
Once I've got mine through it's test (grrrr ABS grrrr vagcom grrrr) and escaped back down south to yorkshire I don't mind taking a look if you put the kettle on. No promises though!