Sorry for the misunderstanding.
@FlyboyZR1 As far as wiring, it's hard to say knowing what you have installed. I would show you mine, but mine has a dual battery setup, with a dual battery battery tender and some extra wiring to feed my amp and run into a 2-battery switch.
That said, using
@go_panthers picture, the positive lead of the battery is being connected to the main battery cut off switch. The brown, larger gauge (thin wire) is tied to the same lead that the main battery (+) lead is connected to, meaning it will alway be connected to the + end of the battery, even though it isn't directly connected to the battery. The way the battery switch work isn't setup to be the connection between positive and negative of the battery. It's connecting the + end of the battery to the rest of the electrical system. Same thing as just removing all the cables on just the positive end of the battery, which opens the circuit and wont work. But again, since the pump wire is connected to the same side as the live battery lead, it isn't affected by the switch. You could do the same thing, installing a switch on the negative side of the battery, but you don't as it could be dangerous if you only had a ground switch. If you have the current switch configured, no need to have the switch to ground and just wire all the ground circuit wires to the (-) lead of the battery.
As far as grounding, as you may not see an equally thing wire for the pump, there are multiple grounding points throughout the circuit. There's a grounding bus behind the helm for the dashboard circuits and another for the engines. The bilge pump isn't pulling that much current to require thick cables and need to be directly connected to the (-) lead of the battery. It's probably connected to some ground bus on the engine, i'd have to go check, but where it's connected to isnt important, as long as it's connected to SOME ground. To make sure it's always on, it's has to be connected to the (+) lead, which you just need to check the wire at the switch to see if it's there.
Looking back at your post, how much water was in the bilge and approximately how long did you have the bilge pump on till it couldn't pump out any water? I've cleaned the inside of my boat with a hose and filled up the bilge more than I would on the water and the bilge didn't automatically kick in. Only when I hit a large wave and accumulated a lot of water did it kick in. Most often, after a day of use, water will collect in the bilge. But if you had the bilge pump on for a few minutes, than it may be a bad sensor. I can take a look at the sensor and see how it works and see if it's easy to give a false water level reading.
