Dash Oil and Brake Warning light - how are they triggered in the start function?

jos51700 said

I think the oil pressure switch grounds the circuit, and oil pressure moves the contact and breaks the ground so light goes out.

Power to the circuit turns off with the key

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Then you show me where it gets power. IGN1 goes dead during cranking. It may get some power fed back through the ballast resistor backwards during cranking. But you are talking about the battery is down to 11V or less during cranking, the ballast is dropping through the field/ VR circuit and whatever else is on the IGN1 line, so the light can't surely get more than ?? 4V ??

Maybe if you are in a dark/ shaded area opposed to bright sun you will see it. Maybe my engine cranks enough pressure that the starter clicks it right off, or maybe my sender is just more sensitive.

The brake lamp has no ground unless the parking brake is set or the warning/ pressure switch is made, which of course it normally is not.