Abstract: A switch module for connection between a power source and a controlled load, and a method for its operation, the switch module being testable without regard to the nature of the load, the nature of the power source, or whether the switch is actually connected to the power supply and its controlled load. The switch module has two pairs of MOS FET solid state switches, each pair connected back-to-back to allow switching of alternating current (ac) as well as direct current (dc) in either direction. Each pair of switches in the module has an associated independent power source, which is used in the preferred embodiment of the invention to supply a control signal to each switch and to supply a test current through the switch when it is closed. Test pulses invert the state of each switch momentarily and corresponding test current pulses are observed if a switch is operating properly.