The Mercedes-Benz GLA250 tail light requires a bulb size of 921 for the specific lighting component located at the rear of the vehicle. Data for the bulb specifications covers the range from 2017 to 2020.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 921 bulb is the sole outer tail light bulb type listed for the Mercedes-Benz GLA250 across the 2015-2020 model years.
The 921 bulb follows the ANSI standard, which is the recognized specification framework used in the United States and Canada for automotive lighting components.
It is a wedge-type bulb, classified under the T15 designation. The T15 designation refers to the bulb's tubular shape, with the numerical portion indicating a width of 15 eighths of an inch.
The 921 operates at 12 volts and draws 16 watts, which are standard low-voltage values consistent with typical automotive electrical systems.
The wedge base design means the bulb is held in place by tension from the socket itself rather than by a separate bayonet or screw mechanism, which affects how the unit is seated and removed.
The 2020 model year entry explicitly notes a Halogen designation alongside the 921 bulb size, indicating that the outer tail light assembly for that year uses a halogen light source rather than an LED or other technology.
The 921 bulb type is widely used across multiple vehicle makes and models, which means physically compatible substitutes may exist, though electrical and photometric output should match the 16W rating to maintain proper function.
Because the 921 is an ANSI-standardized bulb, it is subject to defined tolerances for base fit and electrical characteristics, which supports consistent interchangeability among bulbs carrying that designation from different manufacturers.