Brake pressure warning switch Options

[SVG223]

In the middle of rebuilding/bleeding the brakes and the parking brake warning light is flashing while doing test drives and won't shut off. After checking the parking brake switch I do a little research and read about the brake pressure warning switch on the master cylinder which has a reset button. I'm thinking about how often I might have to reset the thing before I'm done with the brakes. What about cutting the wire to the switch until I decide to rebuild/replace the master cylinder, then reattach it? I don't think I need a flashing light to tell me that I have low brake pressure, that should be obvious.

[GregAmy]

It is a pin switch that works on the central shuttle valve. That shuttle valve moves from its center based on differential pressure between the front and rear circuit. If one circuit has pressure and the other does not (or has significantly lower pressure) then the shuttle valve moves toward the low side, activating the pin switch. The light comes on, telling you one of your circuits has low brake pressure.

Once you fully bleed both circuits, the shuttle valve auto-centers, the pin switch is deactivated, and the light goes off.

So if you're driving the car and the brake light is coming on, then either you have a damaged master cylinder or one of your brake circuits is faulty.

BTW, technically there should be no brake fluid in that center of the master cylinder body where the shuttle valve is. You can remove/replace that switch and not have to re-bleed the system. But, some fluid may leak by the seals so that's why many switches will have a weep hole. but if you pull that switch and there's a lot of fluid in there then you have a faulty master cylinder. - GA