Part number question for 1972 Thunderbird

I need a new reverse light switch. The number I need is D2SZ 15520 C. This is for a 1972 Thunderbird with 460ci engine. I just don't know about the last letter. I am unable to remove the old part at this time so I am guessing.

It is electric and vacuum, the light comes on when the car is placed in revers and it also releases the parking break.

The breakdown is D=1970's, 2=Last year digit, S=Thunderbird, Z=Ford Part, 15520=Part number, C=Specific application.

I have been told the C is for the electric and vacuum application. Now, I found one with an A.

Can anyone explain the last letter?

I know some matter because of a date cut off. One is before 9/71 and one is for after 9/71.

Thanks,
Mark

I was able to remove the old part and the number is D2SA15520-AJSX under it is says BP.

Thanks again