Abstract: A locking marker cap has structural features to snap lock to various types of a tool-less insulation displacement connector (TIDC). When the cap is attached to the TIDC, additional structural features of the cap lock a latch of the TIDC in a closed position to protect the TIDC from being accidentally opened and coincidentally disconnecting the circuit served by the TIDC. In one embodiment, the cap must be removed before the TIDC can be unlatched and opened. At least a top surface of the cap can include indicia such as a color, letter(s) or symbol(s) to indicate a type of circuit served by the protected TIDC.