In the interest of keeping busy, I started going through the ML as it's filthy inside and has a few electrical gremlins.
Found and fixed the corrosion causing a taillight bulb warning and established the cause of the number plate bulbs not working.
Then removed all the boot trim, partly to clean it and partly to access the fuel tank sender wiring as the gauge doesn't work. Found evidence of mice having chewed up the sound deadening foam behind the boot side panels...

Then replaced the non working light sensor for the auto lights along with the overhead control panel as the one in the car had obvious issues including a burnt out bulb that had damaged the lens so it looked pretty manky. Turns out the reason the bulb had failed was because said mice were using the back of it as a toilet. Which also explained why the auto lights had stopped working... The panel is an ECU on the body CANBUS and this failure could also be behind the battery drain that the previous owner had solved by pulling the radio fuse but I will investigate that separately.