So it WAS working and now it's not? Or has it ever worked on your watch? If it's never worked...hard telling what a Previous owner might have done re the wiring.
I apologize if you've already done all this but it's what I would do:
Check with a multimeter to be sure there is power present at the output side of the breaker. Assuming there is power at the breaker screw, touch the probe to the bare part of the wire that connects to the breaker terminal to ensure there is power getting to the wire. If not then the connection at the breaker may have corroded. Break/clean/remake the connection.
Then check the breaker-to pump wire at the pump buss. Is there power at the terminal? Sounds like "no" from your post but could have been the connection at the breaker. If no power, again, check the bare part of the wire that attaches to the terminal. IF power is there, clean the terminal connections.
If NO power is there then obviously there is a break in the wiring between the breaker and the pump buss. It could be an actual break, corrosion internally that has broken the connection, an overheated with that has burned through, or a bad intermediate splice/connection.
