Hummer H3T Map Light Bulb Size

The Hummer H3T map light requires a 578 bulb size for the interior lighting system. Data for the specific component covers the range from 2009 to 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
2009-2010	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 578 bulb is the map light fitment for the Hummer H3T across the 2009-2010 model years.
The 578 is classified as a festoon-type bulb, meaning it is cylindrical in shape and makes electrical contact through metal caps at each end rather than through a base socket.
The 578 bulb has a nominal length of 41mm, which is the span between its two end-cap contacts and determines physical fitment within the festoon holder.
It operates at 12 volts and draws 12 watts, figures consistent with standard automotive interior lighting circuits.
The 578 designation follows ANSI standards recognized in both the United States and Canada, indicating a standardized specification rather than a proprietary part number.