Check the listing for details. 71-77 Disc Brake Proportioning Combination Block Valve Switch Brass Cast Lead. Condition: New, Made in United States. Listed at 20.00 USD. Inline tube - PR102A - 71-77 GM Factory Disc Brake Proportioning Valve Correct Switch.This is the switch only that is in the top of the Prop. Valve of all 71-77 GM cars. Your brake warning light lead plugs in and if there is a loss of pressure a warning light in the dash will be on. THE PROBLEM: When you buy an after market valve from one of the disc brake companies you get the 78 and newer valve with the plastic lead, so your existing wiring plug will not work so now you have to buy a new lead and splice it in or leave the wire off. Now you can buy the right part and screw it in, snap on your lead and be done. The best part is it will look correct and save you a bunch of time. This part is for all the brass 5 port valves that the conversion.