Western Maryland 75 is an electrical beast, and there are several "power contactors" which make electrical connections to the traction motors, and connect the battery to the main generator for engine start. I was asked to take a look at these, because they had been acting up, with the result that not all traction motors were engaging.
The red things on the top are "arc chutes". P2 is removed so you can see. On either side are metal pieces that serve as parts of a magnet. In the back of the contactor, the main power cable loops around a bolt a couple times. Magnetism is rated in "ampere-turns", and with these big amps, just 1 or 2 turns makes a lot of magnetism. The bolt attaches to those metal plates, which act like a magnet. When the contactor breaks (opens), current wants to keep flowing, and will leap across the contact points in a burning arc. The magnet's job is to bend that arc so it goes up into the arc chute and extinguishes itself.
Anyway, along the bottom of the contactors is what are called "interlocks". All of the ones on P1 through P4 are "normally open", meaning they don't connect until the contactor does. The GS1 and GS2 interlocks are "normally closed", meaning when the contactor operates, they disconnect. In this case, that's to disable things that should not run while you're cranking an engine, notably auxiliary generators and traction motors.
As you can see, they are pretty irregular. I worked on them for a couple of days to clean them up.
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