[losvedir]

Also not a pilot but I don't think you can switch the wheel off. You can, however, disable the electric motors that spin the wheel, which is what the checklist for runaway trim tells you to do, and what was supposed to have been done here.

[WalterBright]

The spinning wheels are directly connected to the stab trim via cables. If the trim motors fail, the pilots can turn those wheels by hand (there's a folding crank on them) to manually adjust the trim.