Ram 3500 Map Light Bulb Size

Additional Notes

• The Ram 3500 map light specifications cover two bulb types across the listed model years: the 212-2 and the 578. Both are festoon-style bulbs operating at 12 volts and 12 watts, with a 41mm length.
• The 578 bulb is specified for the Ram 3500 across the 2013-2020 model years, making it the more frequently listed bulb type in these specifications.
• The 212-2 bulb appears in the 2011-2012 model years and again in 2023, indicating its use at both ends of the listed production range.
• Although the 212-2 and 578 share the same voltage, wattage, and festoon form factor, they differ in base design. The 212-2 uses an SV8.5 base, while the 578 uses end-cap contacts. These two types are not interchangeable despite their physical similarities.
• The SV8.5 base on the 212-2 bulb features a metal collar that seats into a specific socket type, whereas the 578 relies on direct contact at each end of the glass tube. Installing the wrong type risks a poor electrical connection or fitment failure.
• Both bulb types conform to ANSI standards recognized in the United States and Canada, meaning they follow a defined specification for electrical and physical performance within those markets.
• At 12 watts, both bulbs fall within the low-wattage range typical of interior courtesy and reading lamp applications, where heat output and current draw are kept minimal.
• The Ram 3500 (2023) uses the 212-2 bulb, which shares its specification with the 2011-2012 model years, though the intervening years from 2013 through 2020 are listed with the 578 instead.