There should be a diagram of how the switch works on the switch. If the pic below is the switch you have here is the diagram of how it works as well.
This is two switch's in one and they both work at the same time in parallel
S1=switch 1
S2=switch 2
S1C= the common terminal for switch 1 (input)
S1A= 1 of two possible out puts for switch 1
S1B= the second of two out puts for switch 1
S2C= the common terminal for switch 2 (input)
S2A= 1 of two possible out puts for switch 2
S2B= the second of two out puts for switch 2
In the on position.
S1C=S1A
S2C=S2A
In the off position.
S1C=S1B
S2C=S2B
So if you are only using this for the pump connect you pos wire from the battery to S1C and the pos from the pump to S1A and connect the neg from the battery directly to the neg of the pump.
Travis