You must have a battery or a dummy installed. Also change the secondary 9V PP9 battery.
About power supplies:
The original power adapter (M5136) for the Portable provides a modest output -- 1.5A at 7.5V, a nominal 11W. The adapter's output is not sufficient to recharge a heavily discharged battery and to run the Portable simultaneously. The PowerBook 100 power adapter (M5140) provides a nominal output of 15W and is more effective at recharging heavily discharged Portable batteries. Later PowerBook adapters provide outputs that are too great to use safely with a Portable. The Portable may run briefly, but the life span of its electronics will be shortened. Apple sold an external charger for Portable batteries that allowed them to be recharged outside the computer but this appears to be rare.
About power supplies:
The original power adapter (M5136) for the Portable provides a modest output -- 1.5A at 7.5V, a nominal 11W. The adapter's output is not sufficient to recharge a heavily discharged battery and to run the Portable simultaneously. The PowerBook 100 power adapter (M5140) provides a nominal output of 15W and is more effective at recharging heavily discharged Portable batteries. Later PowerBook adapters provide outputs that are too great to use safely with a Portable. The Portable may run briefly, but the life span of its electronics will be shortened. Apple sold an external charger for Portable batteries that allowed them to be recharged outside the computer but this appears to be rare.