Brother HL-7050N - Manual (Page 146)

OPTIONS 4 - 19
HL7050_US_UG_FM5.5
5 Connect the longer hard disk cable to the HDD with the keyed
side facing up.
Figure 4-19
6 Install the HDD base plate by putting the four screws into the
four holes of the metal plate so that the HDD pins point to the
back of the printer. Then secure the plate with the four screws.
Figure 4-20