MG MGB front and rear side marker bulbs utilize 257 and 1895 bulb sizes across the vehicle's lighting system. 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 MG MGB uses two distinct bulb types across its side marker positions: the 1895 and the 257, both of which are ANSI-standard bulbs recognized in the US and Canada.
The 1895 is a miniature wedge bulb in a T5 form factor, rated at 12V and 0.9W, and it serves as the front and rear side marker bulb on the MG MGB for model years 1969-1979.
The T5 designation on the 1895 bulb refers to a tubular glass envelope that is 5/8 of an inch wide, a common sizing convention in miniature automotive lighting.
The 257 is rated at 12V and 2W, making it more than twice the wattage of the 1895, and it accommodates either a festoon or BA9s base configuration.
A festoon base bulb is cylindrical with contact points at each end, while a BA9s is a small single-contact bayonet base. The 257 is listed as compatible with both mounting types.
For the 1980 MG MGB, both the front and rear side marker positions require the 257 bulb rather than the 1895 used in prior years, indicating a socket or housing change for that model year.
The 1895 and 257 are not interchangeable. Beyond their wattage difference, they use different base types, and substituting one for the other would require a socket that physically accepts the replacement bulb.
The front and rear side marker positions on the MG MGB share the same bulb specification for every model year covered, meaning no distinction exists between front and rear requirements within a given year.