as the main part number is the same with an A at the end it would denote that it is the first revision of the part but will work in place of the original
If it were me I would get it
Hd parts get a revision letter if the part supplier is changed or improvements are made to the part
From HD current revision is C
32478-99C
This part supersedes the following part numbers:
32478-99
32478-99A
32478-99B
Click the part number to see details
IGNITION MODULE, TC88 ALPHA
Brian