The correct answer is D) No voltage on the output of the secondary coil. An open primary coil in a simple potential transformer will result in no voltage being induced in the secondary coil, as the primary circuit is broken and no magnetic flux is being generated to induce a voltage in the secondary. This is the key indication of an open primary coil - the absence of any output voltage on the secondary side. The other options are incorrect because: A) An infinite resistance value would indicate an open circuit, not specifically an open primary coil. B) An overloaded secondary coil would not be an indication of an open primary. C) A low resistance value on the primary coil would not necessarily indicate an open circuit.