IBM THINKPAD 72 W DC - Manual (Page 8)

Using the power adapter
You can connect the power adapter to an automobile cigarette-lighter socket or
to a 4-pin power receptacle in an EMPOWER in-flight power system.
Connecting the power adapter to a cigarette-lighter socket
To use the power adapter with a cigarette-lighter socket, use the following
steps.
Step 1
Insert the smaller, yellow-tipped connector into the power connector of your
ThinkPad computer.
1-2 ThinkPad 72 W DC Power Adapter: User’s Guide