Ford F-250 Map Light Bulb Size

The Ford F-250 map light utilizes bulb size 578 and bulb size 105 for interior illumination. Available information covers the specific time range from 1985 through 1999.

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
1997-1999	578
1988-1996	105
1985-1986	105

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, 41mm length, end-cap contacts. 12V, 12W.	578
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 13W.	105

Other Locations

Additional Notes

The Ford F-250 map light uses two distinct bulb types across its model years: the 578 festoon bulb and the 105 bayonet-base bulb.
The 578 bulb is an ANSI-standard festoon type rated at 12V and 12W, with a 41mm length and end-cap contacts that seat into spring-loaded holders at each end of the socket.
The 105 bulb is an ANSI-standard single-filament type rated at 12V and 13W, fitted with a BA15s bayonet base, and is classified as a variant of the widely used 1156 bulb family.
The Ford F-250 (1997-1999) takes the 578 festoon bulb for the map light position.
The 105 bulb is specified for the map light across the 1985-1996 model years, with the exception of 1987, which is not present in the specifications.
The two bulb types are not interchangeable, as the 578 uses end-cap contacts while the 105 uses a BA15s bayonet base, representing fundamentally different socket designs.
A bayonet base, such as the BA15s on the 105 bulb, is a twist-lock mounting style where pins on the bulb base engage slots in the socket, securing the bulb with a push-and-turn motion.
Festoon bulbs like the 578 are held in place by tension from the socket contacts rather than a locking base, making socket compatibility dependent on both the bulb length and contact style.
Although the 105 is described as a variant of the 1156, the two are not confirmed as direct substitutes in these specifications, and the 105 designation is the one listed for this application.
Both the 578 and 105 are ANSI-standard bulbs recognized in the US and Canada, meaning they conform to a shared North American specification for bulb coding and electrical ratings.