Well after much work, the problem is a micro switch.
Electrically, it's a very simple module. It really is nothing more than microswitches and a small motor, that's it.
Some solder joints were dodgy and were re-soldered, the micro switch I cut out, to get me out of trouble for now. The switch says the door is open when the contacts are closed, so cutting it out will stop the contsant 'beep drivers door open' and the fuel pump from priming 100 times a day.
Just chucking it back together, reckon I'll leave the door card off as when I put it on I couldn't open the door from inside as for some reason there's some slack on the steel cable that goes to the mechanics of the lock. Pulling the end of the cable opens the door, but I have to pull it further.
Don't know if I can get this actual micro switch that will fit properly, so I may well have to just get a new module, but was worth a try.