IBM System/370 Operator's Reference Manual page 41

TEST indicator
STORE-STATUS key
MANUAL indicator
WAIT indicator
CHECK-STOP indicator
Goes on when a manual control is not in its normal
position or when a maintenance function is being
performed for the CPU, channels, or storage_
I nitiates store-status function_ Function initiated on
some models by pushbutton, on others by use of a
special keyboard mnemonic or by CRT-menu selec-
tion_ Effective only when CPU is in stopped state_
Goes on when CPU is in stopped state_
Goes on when the CPU is in the wait state_
Goes on when the CPU is in the check-stop state_ A
CPU reset will tum it off.
THERMALICB POWER-CHECK Goes on when a thermal condition or a circuit-breaker
indicator
SYSTEM indicator
Page 3-2
trip, or both, are detected in the CPU complex.
Turned off from CE power control panel.
Goes on when the CPU cluster meter or customer-
engineer meter is running.