Mercury Mariner Dome Light Bulb Size

The Mercury Mariner dome light requires a bulb size of 578 for the interior lighting system. Data for the specified component covers the range from 2005 through 2011.

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
2005-2011	578

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, 41mm length, end-cap contacts. 12V, 12W.	578

Other Locations

Additional Notes

The Mercury Mariner uses the 578 bulb size for the dome light across all model years covered in the specifications, spanning 2005-2011.
The 578 is a festoon-style bulb, meaning it is cylindrical in shape and makes electrical contact through metal caps at each end rather than through a base socket.
Festoon bulbs are held in place by spring-loaded clips within the dome light housing, with the end caps pressing against the contacts to complete the circuit.
The 578 bulb has a length of 41mm, which is the critical fitment factor for festoon bulbs, as the housing clip spacing must match the bulb length for proper contact and retention.
The 578 operates at 12 volts and 12 watts, which is consistent with standard automotive electrical systems.
The 578 designation follows ANSI standards recognized in both the United States and Canada, indicating a standardized specification shared across North American markets.
Because the 578 is an ANSI-standardized type, it is produced by multiple manufacturers, and physical and electrical compatibility is governed by that standard rather than by brand.
Festoon bulbs of the same length are not always electrically interchangeable, as wattage ratings can differ between bulbs sharing the 41mm form factor, making the 578 designation the reliable reference for a correct replacement.