I'm not up to speed on Irish geography or traffic laws: is that right hand drive or left hand drive? It may not matter much, but helps clarify "drivers" vs left or right. I checked my US-spec '83 diesel and I only have one door contact on either side. I also checked the wiring diagrams for 230E's and don't see a second door switch, but they're not super-user friendly documents.

I'm speculating here: but is there an aftermarket alarm or immobilizer added? That may be the second door contact.

Two suggestions - if possible, remove and clean the lower door contact. You may want to disconnect the battery first since your wiring may be a bit wacky and you don't know how much current is actually going through the circuit (I'd double-check for the aftermarket alarm, because you may end up really immobilizing your car if you end up disabling that).

Pull fuse 14 and see what happens (I think 14 is the "warning circuit" fuse and that may eliminate the reverse path).

I think you may have a relay that is sticking and creating a reverse current path that keeps the ignition switch energized. That may explain the lights and the shutdown.