المرحّل مرتخٍ في مقبسه

A relay not fully seated, so its contacts make intermittently. It is mechanical rather than electrical, and it is one of the few faults that can be fixed by pushing something in — which is precisely why it is worth checking before anything is measured.

The behaviour is intermittent in a way that follows vibration, so the controlled device works, then does not, then does — often changing over a speed bump or with under-bonnet temperature. A fault that clears when the fuse box is disturbed during diagnosis has been found and lost in the same moment, and that observation is the diagnosis.

Sockets lose tension with heat and repeated removal, and a relay swapped during earlier testing is frequently the one left proud. Check each relay is fully home and that the socket grips — a relay that can be lifted with light finger pressure is not making reliably. Spread or corroded socket terminals are the other half, and they cannot be fixed by reseating.