Can anybody tell me why my brake light on the dash says on if i unplug the proportioning valve wire the light goes off. Its not the emergency brake i just replaced the assembly light still on thanks for any help

 

Then its the brake switch in the distribution block/proportioning valve. Someone just had this same issue. They took their block apart and cleaned it and that fixed the issue.

 

Yes, the earlier "all drum" brake warning switch is simply a piston that is normally centered, holding the warning switch OFF

A decrease of pressure in one end or other of the brake system will cause the piston to shuttle to one end or t' other, turning on the switch.

Some later valves combined this warning function with a proportioning valve, as well as both types acting as a distribution manifold or "block."

I would agree that after 30-40 years, they might just be gummed up inside.

 

Make sure to check your brake fluid and bleed your brakes if needed....check wheel cylinders and make sure there are no leaks in the system... the light coming on is normally also associated with your pedal almost going to the floor under normal operation.