IBM 704 - Manual (Page 276)

Troubleshooting
Identifying Problems through Status Indicators
Status indicators on the server can help to identify problems with
some system components such as power supplies and hot-swap
drives.
Power Supply Status Indicators
To recognize the state of the power supply, you must examine the
following indicators:
Green Power-on LED on the front of the server
Amber Power-fail LED on the front of the server
Power Supply OK LED on the back of the power supply
Current OK LED on the back of the power supply
When the server is lightly loaded, that is, when some of the adapter
slots and drive bays are not filled, the power supply might continue
to function properly, even when the status indicators show a
problem.
258 PC Server 704 User's Handbook