Next thing, the radio.
It would fire up and then switch off without actually doing anything and would kill the battery overnight.
The head unit, audio gateway, CD changer and Bluetooth ECU are all connected by a fibre optic loop. Switching the HU on triggers a loop check by the audio gateway. This keeps going until each component checks in. Unfortunately in this generation of Comand, the audio gateway is integral to the HU. The loop checked out at each point outside the HU, ruling out the CD changer and Bluetooth ECU as the faulty component. Basically the HU wasn't seeing itself, so shut back down whilst the audio gateway kept trying to perform the roll call, hence the drain.
Having established the likely culprit, a known good unit was acquired from a private seller and the radio, including NAV now works at it should... But...
It came from a car without the CD changer or phone pre wiring, so whilst my phone pairs to the Bluetooth, the radio doesn't know it's there. Same with the CD changer. Fix one thing...

All is not lost as it should be possible to recode it for both. And as Pandora has her box open, I may as well retrofit a reversing camera and code that in at the same time.
Whilst we're in the electrics...
The Climate Control functions except for the aircon. Regas first and go from there.
The non functioning parking sensors are down to no signal from one rear sensor. These are a newer version of the system fitted to the Omega but with visual warnings as well as the beeps. Trouble shooting should be straightforward... Common power and ground to all the sensors in each bumper along with a single signal wire to each sensor. Checking this to the ECU will be relatively straightforward thanks to the wiring diagrams on WIS so if it's rodent related it's just a question of running one wire from the boot connector to the ECU. However, just in case it's the bumper loom or sensor, I have acquired both.
Towbar wiring has been removed as there's absolutely zero point using scotch blocks when you can get a plug in harness.
The shin breaker is being replaced with a factory fold away tow ball like the one on TPC along with the correct harness.This will be a relatively straightforward job as well and a bit of
box ticking coding should see that all ticketyboo. Just waiting on bits for that job, and whilst the bumpers off, I can further investigate the parking sensors.