What causes the cabin light not to turn on when opening the car door?

[ORiley]

The reason the cabin light does not turn on when opening the car door is due to switch failure or bulb failure. Specific details are as follows: Switch failure: Over time, the switch may wear out, develop poor contact, corrode, or age, leading to the rear light not turning on or poor contact. The detection method involves setting the multimeter to the 200V voltage range, locating the light wire, and inserting the two probes into the positive and negative terminals of the light wire. Turn on the power and operate the switch to see if there is voltage display. If there is no display, the switch may be faulty. Locate the headlight switch wire and use a wire or metal tweezers to short-circuit the switch wire. If the light turns on, it indicates the switch is faulty. Bulb failure: Most bulbs are "filament-type" bulbs. Driving on uneven roads for a long time or prolonged use can cause the internal filament to break or burn out, resulting in the light not turning on. The detection method involves unscrewing the bulb and observing whether the filament is broken. Typically, the bulb has two filaments—one for the headlight and one for the brake light. If one of them is broken, it is likely the bulb.