IBM 72W AC User Manual page 18

adapter power cord does not work with your adapter contact IBM
Service and Support for a replacement adapter.
b. Automobile / Airplane Mode: If DC output LED indicator is not
illuminated try connecting the adapter to an AC power source. If
adapter does not work in AC mode contact IBM Service and Support
for replacement adapter. If the adapter works in AC mode contact IBM
Service and Support for replacement In Flight Power Cable /
Automobile Power Receptacle Adapter. If the replacement cable does
not work with the adapter contact IBM Service and Support for a
replacement adapter.
7. Connect the adapter to your ThinkPad.
a. If the adapter immediately shuts off check your ThinkPad's power
connector for looseness or damage. Try connecting the original AC
adapter to your ThinkPad. If the original AC adapter operates correctly
contact IBM Service and Support for a replacement adapter.
b. If the adapter works for a period of time and then shuts off check to
insure the adapter has proper ventilation. It is normal for the adapter to
get warm to touch.
c. If the adapter is used in the Automobile Mode while the engine is off
and the adapter shuts off after a period of time, contact an automotive
electrical technician to check your vehicle's electrical system for proper
output voltage with the adapter and your ThinkPad connected. Some
automobile manufacturer's designs do not provide sufficient voltage
(minimum 11.5 VDC) to operate the adapter under full load.
Note: The adapter is designed to shutdown and latch off when a fault is
detected. The fault must be removed AND the adapter must be
disconnected from the power source for at least 10 seconds to reset the
adapter.
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IBM ThinkPad 72W AC/DC Combo Adapter: User's Guide