Leitungsbruch in der Türkabeldurchführung

A conductor fractured inside the rubber concertina carrying wiring from the body into a door — the most recognisable fault on any body network, and the first thing to suspect on anything door-related.

The mechanism is simple fatigue. Every circuit reaching a door — the window motor, the lock, the mirror, the speaker, the switches, the courtesy lamp, the door switch — passes through that boot, and the whole bundle flexes each time the door opens. Over a vehicle's life that is tens of thousands of cycles, and copper strands work-harden and break. The break is usually inside the insulation, so the wire looks perfect and only fails a continuity test when it is flexed.

The diagnostic signature is unmistakable once it is known: the fault changes as the door is moved. Something that works with the door open and stops when it closes, or comes and goes as the door is swung, is this. That correlation is worth more than any measurement, and it is available to the owner for free.

Which circuits fail says something too. One broken conductor gives one dead function; several unrelated door functions failing together points at the same bundle rather than at several parts, and is the strong version of the same evidence.

Repair means opening the boot and splicing, and the work is worth doing properly: a bundle that has broken one strand has flexed every other strand the same number of times, so soldered and sleeved repairs with slack left in the loop outlast a quick twist-and-tape by years. Sliding doors and tailgates suffer far worse, since their looms travel further.