Abstract: A self-contained polarity tester (1) tests connection within a device (40), e.g. a lamp fixture, of a power input plug (41) to a socket (53). A tester body (3) has a polarized receptacle (10) which receives the plug (41). A probe (20) mounted to the tester body (3) is moved by an operator to engage the socket (53). A low-level power source (35) in a circuit in the tester (1) is connected to energize one of a plurality of indicator devices (16, 17) dependent upon the polarity of the connection of the plug (41). Illumination of neither indicator device (16, 17) or both is indicative of a short or open circuit respectively.