Help! I have a 2013 Ducato camper, the side door sometimes will not lock or unlock, I have tried all the usual contact issues, the problem is within the electrics, when in working mode there is a good 12volt kick at the body contacts, when not in the mood to work there is only a small pulse on my meter, the rear and passenger and drivers doors all work fine.

The usual prob is door adjustment, my 66 plate has had the body contact packed out with foam tape and a wedge of wood to push it out closer to the door contact,

If I go too fast around a roundabout the weight of the air in the empty van pushes door out and unlocks!

My Ducato sliding door also came with the top runner already chocked with shims.

I've driven transits that also failed to lock and unlock, similarly to your Ducato. As the sliding mechanism became worn out, I could hear that the lock wasn't even attempting to move.

i shimmed the contacts out with two twent cent pieces one above and one below cheapest fix ive had on the van lol
Cheers Adam