So today I finished off replacing the starter motor - pulled the thorttle body and plenum a week or so ago, then got distracted.
Anyway, also tested my Y cable (alternator-starter-battery) which I replaced around 2018. Cable is good, but there's a short somewhere in the cable to the battery, as there's some continuity with the engine block!
Anyway, I'm OK with car electrics but not a pro, so if there's anyone smart out there let me know how to investigate further!
Starter motor is done at least.