That's a nice switch. For a reversible Simer pump with that SPDT switch, you will need to use relays, which is a much better way to do it anyway, because your high current wires are shorter. If you had 30amp DPDT switches you could do it without the relays, but you would have longer high-current runs.
Use this tried and tested circuit:
http://www.wakeworld.com/MB/Discus/messages/3183/171279.jpg
I believe ground will go to the top-right pin, +12V will go to the left-center pin, then your left-top pin will go to one relay and the left-bottom pin will go to the other relay. Use standard automotive type 12V, 30amp relays, from partsexpress.com or the like.
relays:
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=330-070 sockets:
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=330-075 (Message edited by flsurflover on May 24, 2004)