MT030 Key Lock ON-OFF Isolator Switch — 12V-24V, Red Cover A master switch that anyone can turn is a master switch that can be turned by the wrong person. The MT030 adds a removable key to the familiar two-position rotary format: with the key out, the dial cannot be moved, so the circuit stays isolated while the boat is left on a mooring, the machine sits in an open yard, or the vehicle is parked on a public street. The red cover is not decoration. On a dark dash or inside a