Apparatus for generating an electrical signal which is proportional to the tension in a bridle which supports a string of sucker rod associated with a pumpjack unit. The apparatus includes a main frame having a load cell mounted thereto, and opposed cable engaging arms, one of which extends from the load cell to a cable of the bridle. The two arms place the load cell in compression thereby generating an electrical signal in proportion to the magnitude of the force exerted to spring the spaced parallel cables apart from one another. The signal is utilized to obtain an indirect measurement which is proportional to the tension in the sucker rod. This signal can be combined with another signal related to the position of the walking beam of the pumpjack unit to thereby provide a dynamometer card. The signal is also used as a pump off control which discontinues current flow to the pumpjack motor when the signal assumes a predetermined electrical configuration.