The minus-minus |- -| symbol that you see on the breaker is not negative. Instead, it is the lesser of the positive side. It is referencing the direction of current flow. On these breakers, the plus-plus |+ +| will point to the highest current source, so that could be the solar panel or the battery.

For example, let's assume that your highest current source is the battery. The positive (+) wire from the battery would go into this breaker at the plus-plus |+ +| terminal. Then a wire would come out of the breaker's minus-minus |- -|terminal and into the charge controller's battery positive (+) terminal.

In another example, if your solar panel is the highest current source, then the solar panel would go into this breaker at the plus-plus |+ +| terminal.

If you incorrectly wire the highest current source to the |- -| terminal, the circuit breaker will still trip, however, it may fail and be destroyed after one use instead of the 1000 trips it was designed for, and you would then have to replace it.