Mercury Mountaineer Map Light Bulb Size

The Mercury Mountaineer map light utilizes 168, 578, and 579 bulb sizes depending on the specific production version of the vehicle. Available data covers the period from 1997 through 2010.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2006-2010	168
2002-2005	578
2000-2001	168
1999	579
1997-1998	168

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Miniature wedge bulb (T10). 12V, 4.9W.	168
ANSI standard (US & Canada). Festoon bulb, 41mm length, end-cap contacts. 12V, 12W.	578
ANSI standard (US & Canada). Festoon bulb, 44mm length, end-cap contacts. 12V, 12W.	579

Other Locations

Additional Notes

The Mercury Mountaineer map light draws from three distinct bulb types across its production span: the 168, 578, and 579, all of which conform to ANSI standards recognized in both the United States and Canada.
The 168 is a T10 miniature wedge bulb rated at 12V and 4.9W. Its wedge-style base means it is held in place by friction within the socket rather than by a bayonet or screw mechanism.
The 578 and 579 are both festoon-type bulbs, meaning they are cylindrical in form and make contact at each end via metal caps rather than a base pin or wedge. Both are rated at 12V and 12W, making them significantly higher in wattage than the 168.
The 578 and 579 differ in physical length: the 578 measures 41mm while the 579 measures 44mm. Despite their identical voltage and wattage ratings, the two are not interchangeable due to this difference in length.
The Mercury Mountaineer (1997-2001) uses the 168 bulb for the map light, with the exception of the 2001 model year, which also uses the 168, making the wedge-type bulb the fitment for that early range.
The 1999 Mercury Mountaineer is the only model year in the specifications to use the 579 bulb, setting it apart from all surrounding years.
Model years 2002-2005 use festoon bulbs, with 2002-2004 specifying the 578 and 2005 also specifying the 578, making the 41mm festoon the fitment across that four-year span.
From 2006-2010, the Mercury Mountaineer returns to the 168 wedge bulb for the map light, a fitment consistent with the earliest years in the specifications.
Because the 578 and 579 share the same voltage and wattage, a substitution based on electrical ratings alone would be incorrect; socket length is the determining factor for festoon fitment.
The 168 wedge bulb is the most frequently specified type across the Mercury Mountaineer map light data, covering nine of the fourteen model years listed.