After you connect the external drive (make sure is connected to -disk drive- and not -parallel-) you also need to -mount-the external drive -df1-. to mount it..you need to go to workbench..and from the drawer -i think is expansion, but don't remember-take the -df1- icon and copy paste into the mounted drawer. Basically..move the df1 icon from a drawer to the next, and this will mount the external drive into workbench. Is easy..then it will work.
External Amiga disk drives are autoconfigured to read OFS and FFS disks, you only need drivers if using any other format (like PC0, PC1, DS1) etc.
There is no danger in connecting the disk drive to the wrong port either because the total number of pins is different (23 for Disks, 25 for Parallel)
I suspect that there must be something wrong with the connector, give the solder joints a look over maybe...
