That also happens on mine when I was removing the dash. Had to pull a fuse to turn them off. 2011 4.4 tdv8 Kahn. 2007 supercharged with 2012 lights and overfinch body kit. P38 with a full J.E.Engineering conversion

Hi NDFI,
The light switch is normal behavoir. Have no clue as to the reasoning behind it, but I assume the light switch goes to gnd in the off position (tbh, I've not ever examined exactly what happens within the light switch, tho). Possibly this is just a safeguard to ensure the battery is not drained by making sure you can turn the parking lights off without relying on a message being sent over a bus. This is just my speculating, tho.There is a pic somewhere on the board here of my dash completely taken apart. And if you look closely you'll see my light switch dangling.

I wouldn't worry too much about faults due to removing power from ECUs. Yes, you will log addtl faults. And the worst case is a system, such as the airbags, shut off because the ECU is worrying about blowing an airbag when it is not wanted. I've never powered down an LCM in an early L322 - I will ask the guys if they have any ideas when they get in. It should not cause any serious probs, tho. These systems are all relatively robust as cars go through so much (jump starts, corrosion, etc, etc).

As far as a prob with the bus wiring: I would consider a wire shorting to gnd almost more likely than a corroded connector. Then again, all is possible. And a short to gnd might be even harder to find than a corroded connector...  
RRC 2Dr, RRC 4Dr,
P38, and 2 L322s
(wife thinks I'm nuts - prob right, too)

Thanks both re the sidelights at least I now know that something indicative of a fault.
@Steve, Thanks for your comments it's always useful to have input from someone who has been there before.
I'll just have to slowly plod away on this, a faulty ECU or corrosion I can eventually deal with, a bus cable shorting to earth is a different matter, that really would be awkward to find.

Hi ndfi.
Did you ever manage to find the issue that you had?
I have just checked the voltages on mine and have 10.5v between pins 5&7 and 8 volts between 5&8 with a battery showing 11.5v.
Mine has been a little problematic lately with the turbo blowing, so when replacing that I had the injectors checked and needed all 6 refurbing. Since putting it back together it now has a misfire and I can't access the engine ecu to see what fault codes it's registering.
Oh what fun.
Thanks
Roger.

I am ashamed to say I haven't resolved the problem unfortunately, partially compounded by the fact my car is running well and I have had no reason to date to urgently resolve the issue.
Now the days are getting warmer I will no doubt have another go.
I did come across someone else with the same problem on an L322 who was lucky enough to have the problem resolve itself after a few months, I think I have been waiting for similar divine intervention.
It's interesting you have almost exactly the same pin voltages, I trust you have also checked the earth pins in the socket.

I have only just managed to download rave and look through the wiring diagrams. As far as I can see ports 4 and 5 are earths and will check them. I guess I have been lucky that every fault I have had with my ffrr some one has had before and posted the answer. Maybe this is my time to contribute.
Fingers crossed I will find it and I will let you all know if I find anything.

I wrote a post on this subject under the "electronics section". See the last post in this thread:

http://www.fullfatrr.com/forum/topic23958-15.html ----------
2014 tdv6 (ex. 2004 td6, 1997 2.5 dse)

Thank you for the link I have watched the YouTube clip and checked the connections. Below is what I have on each port.

Pin 1 is 12 volt when ignition is on
Pin 4 is ground (0 ohm resistance to body)
Pin 5 is ground (0 ohm resistance to body)
Pin 7 is signals from engine ecu and automatic gearbox ecu. Should be between 10 and 11 volt.
Pin 8 is signals from transfer box ecu, abs ecu, right headlamp ecu, left headlamp ecu, steering angle sensor and instrument pack. Should be between 3,5 and 4 volt. ( I have 4.1 volt with the ignition off and 8 volt with ign on)
Pin 9 is ground
Pin 16 is 12 volt permanent

I now have the battery disconnected and on charge with the + and -vie terminals connected, just waiting for another mechanic with different diagnostic tester to try it tomorrow.

From my memory pin 8 should have between 3,5 and 4 volt with ignition on. I suggest you start unplugging the ecu's one by one and see if you can isolate where the fault is. ----------
2014 tdv6 (ex. 2004 td6, 1997 2.5 dse)

A bit of an update and a cry for help. I have disconnected the abs ecu , transfer box ecu , LCM module , steering sensor and the headlamp ecu.
The headlamp ecu is situated on the passenger side a pillar behind the kick plate, it is white with a purple plug just below the carpet level.
Anyhow when checking the voltages on port 8 on the odb after unplugging each ecu one at a time it stays the same 8v the only thing left to check is the instrument pack. am I right in thinking this is the clock binnacle ? could a missing MIL light cause this ? as I have never seen it lit. My neighbour who is a lorry mechanic has a Delphi diagnostic tester which also couldn't access the engine ecu.
Could anyone please check the voltage on position 8 of the odb with and without the ignition on? it's the top left connection.
Thanks.
Roger.

I have 6.35V on pin 8 with the ignition off and 8.5V with the ignition on.
The instrument pack ecu is indeed inside the clock binnacle.