The MC pressure switches aren't reliable nor adjustable. You can purchase adjustable pressure switches, but it'll cost x 2 with no guarantee of lifespan. I suggest going retro and install a mechanical switch acting on the brake pedal ala early 911s. Here's an early pedal assy. w/switch. Low tech is reliable as well as adjustable. Also it's easy to hook up a momentary switch to keep potential tailgaters guessing and at a distance. Should be fairly simple to fabricate a switch bracket.
Sherwood