Mount External NTFS USB Drive FreeNAS

Login to FreeNAS via Terminal and run dmesg, you will see a similar output once you plugged in the USB Drive.

ugen3.2:  at usbus3
umass1:  on usbus3
da1 at umass-sim1 bus 1 scbus8 target 0 lun 0
da1:  Fixed Direct Access SCSI-6 device
da1: 40.000MB/s transfers
da1: 3815447MB (976754645 4096 byte sectors: 255H 63S/T 60800C)
da1: quirks=0x2
...

From the above output, we can distinguish the device in question is /dev/da1s1

mkdir /mnt/usb1234
kldload fuse
ntfs-3g /dev/da1 /mnt/usb1234