A switch probe is a spring contact probe and receptacle that is used to verify the presence of components or connectors. The Switch probe is normally open, and after a designated trave the switch probe closes. The most common use for switch probes is in the cable harness testing industry. The switch probe is used to verify the correct location of a terminal contact in a connector while also checking the retention force.
Switch probes also verify the physical presence of non-conductive components such as caps for connectors or devices on a circuit board. There are two separate current paths in a switch probe. From the plunger tip to the tail is normally open and closes only after the probe deflects to the designated travel. The second path, from the plunger tip to the outside of the receptacle, is always closed.