Peterbilt 378 Dome Light Bulb Size

The Peterbilt 378 dome light utilizes a bulb size of 97 for interior illumination. Data for the specified lighting component covers the period from 1988 through 1997.

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
1988-1997	97 (With 2 Rectangular Headlamps)

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 13W.	97

Other Locations

Additional Notes

The bulb size 97 is specified for the dome light across all listed model years of the Peterbilt 378, spanning 1988-1997.
All entries in the specifications carry the qualifier "With 2 Rectangular Headlamps," indicating this fitment applies specifically to that headlamp configuration.
The 97 bulb is an ANSI-standardized type recognized in both the United States and Canada.
It is a single-filament bulb, meaning it serves one lighting function rather than switching between two brightness levels as dual-filament bulbs do.
The 97 bulb uses a BA15s bayonet base, a single-contact bayonet mount that locks into its socket with a twist.
The 97 is noted as a variant of the 1156 bulb. While the two share the BA15s base type, they are not identical, and substitution between them warrants verification of voltage and wattage compatibility before use.
The 97 bulb operates at 12 volts, consistent with standard automotive and commercial truck electrical systems.
At 13 watts, the 97 bulb draws relatively low power, which is typical for interior dome light applications where sustained illumination without significant electrical load is expected.