Seen using 0.10.0.2 on Solaris 11 (compiled from source):
Select +3 machine type, select "48 BASIC" from the menu to enter "locked" 48K mode. Enter "OUT 8189, 255". This results in the disk motor light coming on. Trying the same thing on a real +3, and the disk motor doesn't come on.
I believe the motor running code needs to be hooked into the I/O locking bit (5) of port 7ffd, as the motor can be turned on in "unlocked" mode (i.e. enter +3 BASIC and type SPECTRUM).
I've not yet checked whether the disk controller chip itself is accessible in locked 48k mode.