The Ducati ST4S uses 5008 and 232 bulb sizes for front turn signals and 5008 for rear turn signals. A replacement chart covering 2001 through 2004 model years documents these bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Ducati ST4S uses two distinct bulb types across its front and rear turn signal positions: the 5008 and the 232, both of which are ANSI-standard bulbs rated for the US and Canadian markets.
The 5008 is a single-filament bulb with a BA15s bayonet base, operating at 12V. It is described as a lower wattage variant of the 1156, which is a widely used automotive turn signal bulb sharing the same BA15s base type.
The 232 is a festoon-style bulb with an SV8.5 base, rated at 12V and 3W. Festoon bulbs are cylindrical in form and mount by contact pressure at each end rather than by a base socket, which is a fundamentally different mounting method than the bayonet base used by the 5008.
The rear turn signal position on the Ducati ST4S uses the 5008 bulb across all listed model years, spanning 2001-2004.
The front turn signal position shows a bulb type change between model years. The 2001-2002 front turn signal uses the 232 festoon bulb, while the 2003 front turn signal uses the 5008 bayonet-base bulb.
Because the 232 and 5008 use physically incompatible base types, a festoon socket and a BA15s bayonet socket are not interchangeable, and the correct bulb type must correspond to the specific model year of the front turn signal housing.