We have a very old shallow water water pump that stopped working. It was working before then I turn the whole thing off for a few weeks. When turn it on, I can see the motor turn and running dry. Then the circuit breaks after about 30 seconds. I suspect it need to prime. However, I don't see any priming plug on the pump. The pump is a sears model 390.25320, code number 1c77. Please help.