IBM Personal Computer XT Manual To Operations page 45

Checking Electrical Connections
1
Set the Power switch on the system unit (and
expansion unit, if attached) to Off.
2
Set the Power switches on all attached devices to
Off.
3
Disconnect all devices.
4
Unplug the system unit's (and expansion unit's)
power cord from the wall outlet.
April 1984
Start 20-1