Ram 4500 Map Light Bulb Size

The Ram 4500 map light requires a bulb size of 578 for proper installation and function within the interior overhead lighting housing. Data provided for the specific bulb requirements covers the period from 2013 through 2018.

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
2013-2018	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 Ram 4500 uses the 578 bulb for the map light across the 2013-2018 model years.
The 578 is a festoon-style bulb, meaning it is cylindrical in shape and mounts by pressing its end-cap contacts against spring-loaded holders on both sides of the housing.
The 578 bulb has a length of 41mm, which is a critical fitment factor, as festoon housings are sized to match a specific bulb length.
The 578 operates at 12 volts and draws 12 watts, which is consistent with standard automotive low-voltage electrical systems.
The 578 conforms to ANSI standards recognized in both the United States and Canada, indicating a standardized specification rather than a proprietary or regional-only part.
Festoon bulbs of different lengths share the same mounting style but are not interchangeable, as a bulb that is too short or too long will not make proper contact or will not seat correctly in the housing.