Abstract: An interlock switch for electrically coupling opposing surfaces of a circuit card assembly, wherein each of the surfaces includes a contact pattern defining circuit and switch functions. The interlock switch comprises a pair of contacts which engage the contact patterns on the circuit card assembly to electrically couple the circuits located on the oppositely facing surfaces thereof and a switch body for housing the contacts. The switch body includes a slot for solder-free coupling the switch to an edge of the circuit card assembly. The slot enables the switch to selectively reciprocate among three switch positions on the edge of the circuit card assembly to provide either an open circuit or a closed circuit on the circuit card assembly in any one of three switch positions for each contact. A spring is housed within the switch body for biasing the switch from one of the three positions making it a momentary position.