Graeme wrote:

Well, I think the battery itself is OK. Went for a run Thursday
afternoon to charge the battery, then left it until this morning
(Tuesday) with the earth lead disconnected. Reconnected and an easy
start, from what felt like a still fully charged battery.

To recap, if parked with the battery connected, the battery is almost
flat after 48 hours, as in not enough to turn the engine to start. The
courtesy light switch(es) were suspect, but same thing happens with them
disconnected.

I tried Harry's bulb trick again (small MES panel light bulb between
-ve battery terminal and earth strap), and nothing. Tried using an
ammeter. Nothing. Yet current must be flowing somewhere.
Suspect dynamo control box.

I have a morris 1000 workshop manual somewhere. Send me an email and
I'll try and find the relevant info, scan and send it to you.
Bob