More info on the RR not sleeping in my garage. I persevere because another may find the diagnostics useful in the future, and I would also like to understand this problem rather than just fix it.
I am quite sure that this problem is localised to my garage, and not connected to my recent "Immobiliser/suspect-BeCM" problem or my recent
If I park the 2000 4.6 in the garage, the gear selector light comes on again about 25 seconds after going out. The same thing happens in my driveway or front yard or street front parking.
If it is parked on the other side of the street, it sleeps soundly. If parked at work or a friends, it sleeps soundly.
So, this morning I parked it in the garage, locked it, and then hit the mains to the house and also isolated the solar panels and inverter - all of which are very close to the car outside the garage. She still woke up. I think this means I can rule out my house as the source of the interference.

