Turn off the power supply to your submersible pump motor before testing it. Remove the outer cover on the pump motor by using a screwdriver to remove the screws. Lift off the cover using your hands, once the screws are removed.
Remove the internal waterproof cover that protects the submersible pump motor. Remove the screws from the cover using a screwdriver, then carefully lift off the cover. Do not remove the rubber seal between the motor cover and the base unit; otherwise, water will enter the motor once you replace the cover and put it back in the water.
Locate the two wired terminals on the pump motor. One is labeled "+" for positive the other "-" for negative. Read the label on the side of the pump motor to find out the voltage it uses to operate.
Turn on your voltmeter. Connect the submersible pump to the power supply and turn on the pump.
Test that power is getting to your pump motor using the voltmeter. The voltmeter has two wires connected to it that have metal sensors on the ends. One wire is black for negative; the other red for positive. Place the sensor on the end of the black wire on the negative terminal of the pump motor then place the sensor on the end of the red wire onto the positive terminal of the pump motor.
Read the voltmeter display. If it reads zero, or just above, it means that power isn't getting to the motor, so you need to check and replace the fuse in the plug that connects to the power supply. If you get a reading, it is the same as the labeled voltage on the pump motor and means that power is getting to the motor. Remove the voltmeter sensors from the motor terminals.
Turn the wheel on the pump motor using your hand. If you feel resistance and can't move the wheel, it means that the pump motor is trying to operate but has seized. Turn off the power supply and try turning the wheel again. You can often release it by turning it a few times using your hands.
Turn on the power again to test if the motor operates. If it does, then the problem is solved. If it doesn't, or you are not able to get the wheel to turn, it's likely that there is a fault within the pump motor, which you need to get checked out by a specialist.