Hah, I drew & posted that schematic and posted it in about 2001. Dane modified it to get rid of my unnecessary diode and reposted it, and I've seen it a hundred times since. Cool.
It works for reversible pumps, and is a lot better because it keeps the high amp wires short and out of the dashboard. Just add up the amperage of the pumps that are on each set of relays. They draw about 12A each.