The govt mandated E10 content in gasoline can cause the comutator bars on the motor to corrode if they sit too long.

Try a couple of batteries in series to get more voltage, Pos of battery A to the pump pos, neg of this battery to the pos of battery B, neg of battery B to pump neg.

If this does not work, add another battery to the string. Don't go over 48V unless you use insulated gloves , remote switch as this is the limit to work bare handed.

I recently used 120 VAC house power to jump start a pump in a tank and got it running but a lower voltage should work.

With the pump out of the car, you might be able to use compressed air to get things turning.