Abstract: An improved arrangement for testing the operability of drop wire circuitry associated with yarn handling equipment which does not require yarn movement to be interrupted during tests. A two-position switch operable between normal and test mode positions is included in the circuitry. A jack arrangement is rendered operable with the switch in the test position, thereby permitting an indicator to be selectively inserted in the drop wire circuitry path. The electrical characteristics of the indicator are such as to permit the indicator to be actuated when a drop wire falls while simultaneously disabling the normal response of the remaining drop wire circuitry. Means are provided to selectively bypass the indicator with the switch in the test position to thereby allow the drop wire circuitry to operate as if the switch were in the normal position.