>At all stops, the motorman got a highball from a pilot light when doors closed.

The starting light. The power feed to illuminate this came from the rear car of the rear unit and went all the way forward to the operating cab. This was used at all stops and is a carry-over from the wood cars, where the trainman held down a momentary contact switch after closing the gates on his car. Once all the trainmen held down their switches, the light would go on, signaling the motorman to go. All 900 class city streetcars equipped for MU had the same thing.

All the CTDX (Capitol Corridor and San Joaquin) locomotives, Surfliner, and Amtrak locomotives retrofitted with the "commute pack" have the same thing, where it's called a "door light". The new twist is that the engine won't load until the light comes on. This scheme has become fairly standard with commuter and mid-distance rail services.