MT040 ON-OFF Battery Isolator Switch The MT040 is a two-position master switch for DC wiring that needs a reliable cut-off point. Rotate once to connect, rotate back to isolate — there is no intermediate setting, so nobody has to guess what the dial is doing when the boat is being put away or a technician is working on the loom. Its contact assembly is rated 175 amps continuous and accepts a supply anywhere between 12 and 36 volts, which lets the same part number serve a 12V