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The sensor for the brake lights on the new master cylinder proportioning valve I bought from CJ pony (Oval Master Cylinder With Proportioning Valve Black Aluminum Kit Disc/Drum 1965-1973) only has one wire. How is this wired when I have my two wires to connect?
 

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The single wire connects to a brake warning lamp that is supposed to illuminate if you have a brake failure on one side of the brake hydraulic system. The two wires you are referring to go to the brake light switch, which is under the dash and operates off of the brake pedal. This is for 1967 and later models. The '65/'66 models didn't have the dual bowl hydraulic brake system.
 

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The sensor for the brake lights on the new master cylinder proportioning valve I bought from CJ pony (Oval Master Cylinder With Proportioning Valve Black Aluminum Kit Disc/Drum 1965-1973) only has one wire. How is this wired when I have my two wires to connect?
I'm going to go out on a limb and assume you have an "early" '65 with the brake lamp switch located in the master cylinder.

The switch in the combination valve assembly is NOT a brake lamp switch, it is a brake system warning lamp switch that is activated when the differential pressure shuttle inside the combination switch moves, indicating a pressure loss in one of the brake system circuits.

This system works with a warning lamp in the instrument cluster ('67+) that is wired on one side to an ignition-switch-on power source and the switch in the combination switch grounds the circuit to illuminate the lamp. A splice in the ground-side also runs to a "prove out" terminal in the ignition switch which grounds the circuit when the ignition switch is turned to "start" to test the lamp.

To restore your brake pressure-activated brake lamp switch with the new combination valve, install a brass "tee" between the master cylinder rear circuit outlet port and the combination valve, and insert the switch into one of the ports.
 
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