The “Advanced Format Special Jumper Setting” is just another case where WD’s documentation has been dumbed down so much that it no longer makes any sense.
In fact the jumper does not enable or disable Advanced Format. Instead it adds a +1 sector offset to each logical sector. This means that, when the OS accesses sector X, the drive transparently remaps it to sector X+1.
Windows XP and earlier OS-es begin the first partition at sector 63, a track boundary. However, AF drives have physical sectors consisting of 8 logical sectors, which means that a default XP partition would be misaligned. One solution would be to use a third party tool (eg GParted) to select 64 (or any other multiple of 8) as the starting sector number for the partition. An alternative solution would be to shift the entire partition by 1 sector. That’s what the 7-8 jumper does. Windows XP still thinks that the volume begins at sector 63, but the drive remaps it internally to sector 64.
With the above in mind, there is a relatively simple way to determine if the jumper has any effect. I would use a disc editor (eg DMDE freeware) to write a text string, “Sector 0” to LBA 0, and a second text string, “Sector 1” to LBA 1. Do this with the jumper out. Then power down the drive and install the jumper. Now examine those same two sectors. If their contents remain the same, then the jumper is nonfunctional. Otherwise, if you now see “Sector 1” in LBA 0, then the jumper is working.
In DMDE you would …
select your physical drive
uncheck the Show Partitions checkbox, then OK
select Mode -> Hexadecimal/Text
Edit -> Edit Mode
make your changes
Drive -> Apply Changes
You could also examine word 209 of the of the Identify Device information block with a tool such as CrystalDiskInfo. This should tell you if there is a “logical sector offset within the first physical sector where the first logical sector is placed”.