Topic: 67 backup light housing C7ZZ-15511-A vs C7ZZ-15511-B

[67gta289]

I have a line on a set of C7ZZ-15511-B and C7ZZ-15512-B which according to the MPC was introduced on 4/8/1968.

My car (December 66) should have the -A version.

The backup light document by Marcus (link below) says that the difference was only in the light bulb socket, and there are no external visual differences.

http://anghelrestorations.com/uploads/3/5/1/2/35122002/back_up_lights_v1.1.pdf

Does this mean that the bulb is a different type as well?  If not, why would Ford continue to carry both versions for service?

Thanks

[1967 eight barrel]

No, same 1156 bulb.

[Keith Stem]

The 1157 bulb will fit bulb and work, but the correct bulb is the 1142. The difference is the 1142 is a single filament and the 1157 is a dual filament (Stop and Turn Signal). I did not do a deep research of all years, but it was used in 66 to 68 and probably many more year of first generation Mustangs. 

[67gta289]

Thanks for the replies.

Back to the original question, restated:

If the only difference between the two was a change do the light bulb socket, and if the actual bulb requirements did not change, and if there is no visual difference between the two, then why didn't the revision B part replace the original revision A, instead of carrying both with a running change date?  I suspect that there has to be something more...