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Water reaching an electrical connector, and the single commonest cause of body-network faults on any vehicle — ahead of every electronic failure combined.

It behaves differently from a broken wire, and the difference is the diagnosis. Water conducts, so it does not simply interrupt a circuit; it bridges terminals, creating paths the designer never intended. A module may therefore behave erratically rather than stopping — reporting values that are electrically real and physically impossible — and it typically recovers as things dry out. A fault that follows the weather, appearing in rain and clearing in a dry spell, is this and effectively nothing else.

Then it stops being reversible. Water plus current plus dissimilar metals corrodes the terminal plating, so an intermittent fault becomes a permanent one, and by that point drying the connector no longer helps.

Where it comes from is the part worth pursuing, because replacing the component fixes nothing if the water still arrives. Blocked door drains, torn door vapour barriers, blocked sunroof and convertible drain channels, aged screen and light seals, plenum drains packed with leaf litter, and simple spillage into a footwell all deliver water to places that look dry from outside. Modules live inside doors, under seats and behind trim precisely where those paths end.

The tell is visible the moment somebody unlatches the plug — green or white deposits, dampness, or a terminal that has lost its shine. It is worth asking for explicitly, because a connector is normally checked for being connected rather than for being clean.