| Symptom Behavior | Most Likely Cause | Category | | :--- | :--- | :--- | | No sound, no movement, no dimming lights | Open circuit, dead switch, blown fuse, broken wire | Electrical | | Click or relay sound, but no movement | Motor seized, regulator jammed, low voltage | Mechanical/Electrical | | Slow, grinding, or jerky movement, then stops | Broken cable, stripped plastic gear, worn brushes | Mechanical | | Moves down but not up, or vice versa | Faulty switch contact, broken spring in switch | Switch failure | | Works intermittently or only when door is open | Broken wire inside the door jamb boot | Wiring fatigue |