Hi esteemed friends. I have scoured the internet and failed to even come close to what my E31 problem is... so need serious help!!

My car has been fine for the last 13 years, not one electrical problem, great!! Nothing non standard, no amps, nothing!!
One day, the number plate lights and dash light stayed lit. We found a broken cable coming out of the boot - meeting with a small harness on the side of the boot, and repaired that. All seemed fine.....

About 3 weeks later , went to the parked car only to find the window half down, all ignition lights on (no key in ignition), and no signs of tampering of any kind. The car fired up, but then refused to switch off. Realising a problem potentially with the ignition switch, we removed the fuel pump fuses. Next day the batteries were dead.

Opening the bonnet... revealed the extent of the horror . The cables going from the front distribution box TO the obd.... charred to a pulp.
The OBD connector is jammed shut - but removing it and accessing it from the underside revealed why this is the case.....the cable sheath is gone, and looking at it seems to have melted the data connector (black plastic) hence I cannot remove the cap.

Finally - after I established a problem.. attempting to jump start the car (unfortunately had no access to the battery terminal under the hood and used the left battery... when starting it the cables in the centre console would start smoking. The car was left as is...

I am attaching the pics in the hope someone could shed some light - I have the wiring diagrams, but.... is there any 'correct' approach?

There is a side of that feels close to the 'spontaneous BMW combustion problems' I have heard so much about.

Can anyone help?

Thanks for reading the post... and here is hoping for 'an easy way out'

This is from the left side of console - the red cable clearly melting, with every starting attempt we got little cloud of smoke:

From front dist box heading to OBD connector:

OBD underside - note the melted plastic that has somehow leaked upwards...