When you switch the key to pos II before starting the engine, the warning lights receive battery voltage through the ignition switch and a ground through the small red wire to the alternator that is not turning. You could test this by pulling the small red lead from the tab on the alternator and grounding it while someone looked at the lights.

When the car is running, the alternator raises the voltage on the red wire so the lights go out, unless they receive a ground from the function they are monitoring.

There are diodes in the alternator, rectifying the high current output, found on a large heat sink under the end cover. Also, if someone referred to them, there are steering diodes in the instrument cluster used to facilitate the warning light logic.

The diodes in the alternator are below this plate: