If I mount a proportioning valve prior to the brake warning switch/distribution block, will that cause the switch to stay on. The switch works on pressure difference, so I assume mounting the value prior to that block will cause issues. I can also mount the proportioning value after the block in the line on its way back to the rear brakes, but it would be less convenient. There is a post pretty much saying this, just looking for some confirmation before doing it. Brake Questions - Help So in short, in the clip from the service manual (and pretend there is no metering valve cause its a drum brake car to begin with). If I put the valve where the blue box is, will the warning switch still work? Or does it need to be where the red box is.