Breaker & Wire Size(s) for Controls

Mark, Were are the original breakers and wires?

Mark, You will need to check the amp draw on the fat sac pump and then compare that to the breaker you have. The breaker must be rated higher than the pump but no more than about 100%. Wire must be sized to the breaker size just like wiring in your house. Below is a wire sizing chart out of the West catalog to help you. It does factor in length for voltage drop but you will have a relatively short run. Do use marine wire as it is tin plated so you won't end up with a green corroded copper mess at connections.
Do the spare breakers have factory wired feeds? In other words are they already connected to the hot side of the battery? If they aren't, don't just connect then to anything under the dash. Get back to us here.

Mark, I would adhesive lined heat shrink tubing over your connections. There are also heat shrink Sta-Kons but they may be hard to find. Don't forget about the marine grade wire.