The Mercury Mariner brake light requires 4157 and 3157 bulb sizes for the specific lighting components located at the rear of the vehicle. Data for the provided specifications covers the period from 2005 through 2011.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercury Mariner uses two distinct bulb sizes for its brake lights across its production run, with the 3157 fitted to 2005-2006 models and the 4157 fitted to 2007-2011 models.
Both the 3157 and 4157 are ANSI-standardized dual-filament wedge bulbs of the T25 type, each rated at 12V with a 27W/7W output, where the higher wattage filament serves the brake function and the lower wattage filament serves a secondary function such as running or turn signal operation.
Although the 3157 and 4157 share identical voltage and wattage ratings and the same T25 wedge form, they are not confirmed as interchangeable in these specifications, and substituting one for the other without verification of physical fitment could result in improper installation.
The Center High Mount Stop Light on the Mercury Mariner uses the 12961 bulb across all model years from 2005-2011, making it the only brake-related position with no change in bulb size throughout the vehicle's production span covered here.
The 12961 is a Philips part number designation rather than an ANSI industry-standard code, which means sourcing equivalent bulbs from other manufacturers requires cross-referencing to a compatible T10 miniature wedge bulb with a W2.1x9.5d base.
The 12961 bulb is rated at 12V and 5W, a significantly lower output than the 3157 or 4157 brake bulbs, consistent with its role in a center high mount stop light where a smaller, low-profile light source is typically housed in a compact assembly.
The W2.1x9.5d base designation of the 12961 describes a wedge-type base with a 2.1mm wire contact width and a 9.5mm insertion depth, which is the standard base configuration for T10 miniature wedge bulbs used widely in automotive interior and auxiliary exterior lighting.