By default, you can't. However, you can set up track marks for your AI drivers to follow using the 'Navigate to/via' driver commands, and hence keep them on the right tracks which have overhead wiring/third rails. The simulator doesn't register the overhead wiring as a required power source for the locomotive in any event, hence why it doesn't differentiate between 'electrified' and 'non-energized' trackage.
If you're running an electric loco with an AI driver, the pantograph should go up automatically though as soon as the driver begins his or her assigned tasks.
