A modular test plug for voltage, current and saturation testing has a housing having a handle portion, a plurality of jaw connections for injecting upstream toward the equipment to be tested, a plurality of blade connections for injecting downstream toward a transformer, a first plurality of binding posts on a top of the housing connected to the jaw connections, and a second plurality of binding posts also on a top of the housing connected to the blade connections. Also provided is a short-defeating insert for defeating a shorting mechanism in an FT switch. This insert has a thin flat extension member extending from the body to prevent a bottom cam on a shorting blade from making contact with a shorting spring that would otherwise short the circuit when the switch handle is moved from the open position to the closed position.