Seems I got the colours wrong. I have a blue wire to pin #7 - and also a blue wire from alternator - so that seems to be by the book.
I have a blue/black wire to pin #6 - yet haynes seems to think that 83 300TD should have Blue/Red.
My blue/red wire is wired directly to a 'bulb holder' that was lying in the alternator warning lamp socket
Sorry about my mis-information.
So my question is :- where shopudl my blue/red wire with bulb attached go?