Partner 2003 BSI / BCM / Earth problems...

[Element]

I have an ongoing electrical problem with my Partner 2.0 2003 DW10. Suspect BCM / BSI corrupted. Key in hand, if I open a front door the dash lights up & headlamps come on, key into ignition, turns over but won't start. Wipers come on and off erratically. Have to disconnect battery earth lead to stop draining the battery. Removed BCM but could see no obvious water contamination, no corrosion on any points. Replaced it with another BCM from a 2004 car - made no difference.
BSI - removed that from the car; opened it up to discover very small amount of water on the inside of the base & very slight corrosion (green copper carbonate on 2 of the solder joints on the underside of the pcb). Dried it thoroughly, put it on a radiator overnight, bone dry, reassembled, refitted. Exactly the same symptoms occurred again.

So I am now looking for all the earth points on the vehicle and will remove each, clean and reattach.

Anyone with any similar experience - I'd appreciate your findings (y)

Not only but also... - I have a donor vehicle (2004 model) and as a last resort I could feasibly remove the ECU, BSI & BCM & swap the transponder in the key from the donor 2004 to the original 2003 (I understand that I'd likely then inherit an extra 50k miles as the donor car has done extra mileage but atm I am running out of options..). BUT the donor 2004 has ABS whereas the original 2003 does not have ABS so not sure if that would work out... besides in the 2003 there is no dash light for the ABS.

[GiveMeABreak]

I think you'll be in a world of pain - as the BSI is either the incorrect model and / or has been configured for a different vehicle with different options. This could cause other problems and yes, as soon as you hook it up you'll gain the higher mileage of the 2 vehicles.

I suggest you send the BSI off for a repair to be honest as at least you'll have your original.

[Element]

Yes I figured as much... I have found a company in Norwich that do all cloning, virginising ecu programming services & called them but they said I need to have an auto electrician definitely diagnose the problem before they could accept a BSI. Trouble is - I'm in rural Perthshire and mobile auto electricians are few and far between... So I'm still trying to focus in on the root cause.

[wheeler]

Can you first confirm what you are meaning as some of your terminology is not what i (or PSA) would use.
BSI is the module inside the car
BSM is the under bonnet fuse box
BCM is not terminology normally used on these vehicles but would be the equivalent to the BSI.
Just to clear up what's been replaced.

What is the back story of the fault? just not start one day? Any work done just before the fault happened?

If you have a donor vehicle the first thing i would be doing is swapping the Com2000 module (wiper & lighting stalks), Wipers & lights operating by themselves can mean the com2000 is not talking to the BSI.

Does the Horn work?
Does the central locking work of the remote?
Do you happen to have access to a scope?

There are usually a bunch of earths at both sides under the the kick panel trims.
I will try putting an earth diagram up later.