ok, I'm familiar with this type of electrical connection. Your mains as you describe is the double pullout. The line side goes to the top of the double 60 cartridge fuses. the load side goes to the other pullout for your range circuit. There are two internal jumpers that feed power to the range pullout. NOW that "sidearm" disconnect. The line side you say is connected to where the mains connect in the MAIN box. This is illegal as there is NO protection for the feeders. You are the mercy of whatever is connected to these wires. Your water pump is rated at 240 volts. You don't need a neutral for a single phase 240 volt pump motor. The third wire is used as an equipment ground for short circuit to ground protection. I'll draw up a typical pullout box and the way the sidearm feeder should be connected. Just gimme a few days. I'll include the sidearm and typical porcelain fuseblocks. If by the way you're thinking of upgrading, the minimum size you can install is a 100 amp service entrance.