Can anybody tell me what the differences are in the Multi Function Modules ?

I have 98AG14K150AF - will other P/Ns work ie ********AE, BG, etc

Later suffix letters do not appear to be later years of manufacture, so it's not that easy.

Headnut

Part number 98AG-14K150-AF has Finis number 1125327 and costs just below €100,-. This is the latest available version of this module. This part number supersedes the following part numbers:

98AG-14K150-AC

98AG-14K150-AD

98AG-14K150-AE

These part numbers are no longer available because they are replaced by the latest part number. These part numbers are basically just older versions of exactly the same part. All part numbers mentioned above are interchangeable.

The first suffix letter of the part number (in this case A) stands for the version of the part. This letter describes certain specifications of the part (supported functions or supported options for example). In most cases this letter needs to be identical.

The second suffix letter of the part number stands for the revision of the part. Every time a part is improved this letter changes. The later the letter in alphabetical order te newer the part.

Sometimes Ford will rationalise the number of parts/modules made available for service meaning that the replacement parts are higher spec but with features that are not used or activated on lower spec cars.

Other than that, JW1982 has covered things pretty well above. The last letter of the suffix will go up in alphabetical order every time a design changed is released on the part. This can happen several times a year, and in some cases you'll never actually see variants released if they're superceded before the previous level is physically introduced. This is due to the inherent delays between changes being released on Ford system and physical parts actually being introduced to the side of the line.