Inline tube - PR100a - 78- GM Factory Disc Brake Proportioning Valve Correct Switch. This is the switch only that is in the top of the Prop. Valve of all 78-86GM cars. Your brake warning light lead plugs in and if there is a loss of pressure a warning light in the will be on. This is exact to Nos in every way even featuring the correct plating and design. These are the details that separate the first place cars from the rest.