Les,
I think you mean 12.7V which should be a bit higher with the charger on but maybe the batteries were just starting to be charged. It sounds like the solenoid switch on the pump is moving but possibly not making contact or it is possible that it is making contact but the motor on the pump is not starting. Let the batteries come up to 13.2V or higher and try it again by pressing the slide button. If the solenoid is not fully making contact then the higher voltage may help. If you still cannot get it to work you can rap on the solenoid and the motor with a light hammer while pressing the slide switch to see if it will start. If it will not work then you will have to seek some service. Ether the required voltage is not getting to the solenoid, or the solenoid is bad, or the pump motor has issues.
Later Ed