Re: Brake warning light ?
I assume your truck is similar to a squarebody in this aspect. On a squarebody, the ignition switch has two pins that are isolated from all others. These two pins are connected to each other in the 'crank' position. One connects to ground, and the other connects to the brake light on the dash.
So basically, the ignition switch is switching the hot for all operations except for this one. In this case, the ignition switch is switching the ground.
The brake light is also grounded through the switch in the proportioning valve. Either the prop valve or the crank position of the key will ground the light.
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