The MG MGB front turn signal bulb uses a 1157 size, while rear turn signal applications accommodate either 1156 or 1157 bulb sizes. The replacement chart covers 1969 to 1980 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 bulb is the most widely used type across these specifications, appearing in the front turn signal position for all listed MG MGB model years from 1969-1979, and in the rear turn signal position from 1969-1975.
The 1157 is a dual-filament bulb operating at 12 volts with a 21W/5W output, meaning it carries two separate filaments serving two distinct brightness levels within a single housing.
The 1157 uses a BAY15d bayonet base, which features two offset pins at different heights to prevent incorrect insertion into the socket.
The 1156 bulb is specified for the rear turn signal position on the MG MGB from 1976-1980, replacing the 1157 that was used in earlier model years for that same position.
The 1156 is a single-filament bulb operating at 12 volts with a 21W output, carrying only one filament compared to the dual-filament design of the 1157.
The 1156 uses a BA15s bayonet base, which has two pins at equal heights, making it physically incompatible with the BAY15d socket used by the 1157 despite the two bulbs sharing a similar overall form.
Both the 1157 and 1156 are ANSI standardized bulb types recognized in the United States and Canada, indicating they conform to a defined set of electrical and physical specifications.
The rear turn signal position on the MG MGB requires two different bulb types depending on the model year, with the 1157 specified for 1969-1975 and the 1156 specified for 1976-1980, making year verification necessary before replacement.
The front and rear turn signal positions on the MG MGB from 1969-1975 both use the 1157 bulb, while from 1976 onward the two positions diverge in their bulb requirements.
Although the 1156 and 1157 share the same 21W high-output filament rating, substituting one for the other is not possible due to the differing base pin configurations of BA15s and BAY15d.