Connected Battery backwards...ouch!

Just a thought. The pump relay may have a reverse diode in it that got fried from the battery being hooked up backwards. Some relays have a diode to prevent back current when the power is removed since the coil will have a kick to it when the power is cut. The collapsing electric field generates a reverse current from the relay coil and the diode stops that. If you fried the diode, you may have an open circuit in the relay and it won't close.