While searching for a solution to my problem (flashing interior lights linked to faulty rear door latch I think), I read many posts about flooded footwells due to the battery drain plug blocked. I decided to check mine and thought I would post the steps - it may help someone....

First step since you are removing the battery is to check you have your radio 4 digit code. Luckily my code was in the BOSE radio manual (photo 1). The code was on page 24 (photo 2).

Disconnect the battery drain/overflow tube (photo 3) then disconnect your battery (negative first of course...)

With the battery out now remove the Battery tray by removing the 2 nuts and 2 bolts that secure it in place, then to remove the actual tray you need to 'encourage' the tray corner past one of the locating bolts (photo 4)

Now you can see the drain plug, pop it out with your finger and clean it (photo 5)

Photo 6 shows the drain removed.

Photo 7 is the actual drain plug itself.

 

Update on door problem: Yes it was the door latch, to be precise; the microswitch was stuck in the door open position, the switch itself was 'gunked up' and cleaning it revealed excessive wear to the contacts. I disconnected the switch, this gives a 'door closed' signal to the ECU I believe, this means everything is fine and my error has cleared. It just means that when I now open the door, the ECU doesn't know.

I have found and ordered 10 new microswitches for $10 on eBay, when they arrive I will fit one and report progress.

 

As promised; repair of Door Micro-switch:

I followed the door latch removal steps I found here - whoops, not allowed to post it, search for 'Door lock repair'

Then removed the micro-switch and used the Dremel (1) to cut off the locating/fastening part (2) to graft onto my new micro-switch (3). I used epoxy to secure it and then adjusted the micro-switch 'clip' (4) to ensure it was held tight onto the door latch assembly. Photo (5) is the adapted new micro-switch ready prior to assembly.

Door works great and no error messages - so far.

With my new knowledge of striping the door and latch down I moved onto the read door as this had decided it would not unlock from the outside - so clearly a problem lurking. I found that the latch circuit board had two dry joints ('cold joints') - hopefully you can see in the photos (10) (11) - zoom if you can and look at the dark ring around the joints - right in the centre, 6 joints - its the left 2 that are faulty. I soldered these up and the repair was complete without issues.

And for clarity I've added some photos of the actual latch and the original fault micro-switch...