1967 Ford Mustang Brake light on dash function?

It's likely the brake warning light that lights up when you have a leak, have wrong pressure going to the calipers/wheel cylinders, or when the proportioning valve is worn out or malfunctioning. It may light up for a few seconds when you first start the car. This is normal. There is a plug on the proportioning valve that will send a signal to stay lit when there is a problem with the brakes.

If it's coming on when the engine is first started that is a problem that could be the brakes themselves or a wiring issue. There is a "cold" light in the dash of my 1967 Fairlane that lights up for a few minutes until the engine warms. Maybe the wiring has been messed with. If you have a temperature sending unit with two prongs on it then you may have a cold dash light as well. To test if it's actually the brakes, simply unplug the connector from the proportioning valve and see if it stops lighting up. If not, then it's not your brakes. Then unplug the connector from the temp sending unit. If it stops lighting up in the dash then you have something plugged in wrong or miswired.

1967 Mustang Dash

My first concept is the brake change. additionally examine the connections. clean off the connections utilising sand paper to confirm solid contacts inclusive of the floor wires for the circuit. solid good fortune you're able to desire to consistently bag the entire equipment and order a "Painless" wiring kit.