As I read this again this morning, I may have been a little too brief to be clear in my first response.
Electricity basically flows from pos to neg. A circuit breaker or fuse protects everything downstream of itself. If the fuse blows on the way back to the battery
because it's in the negative line right at the battery, all the wires prior to the fuse are still live and could be shorted to some alternative ground. There are all sort of things you could short to while trying to fix what is wrong.
Keep in mind that the circuit breaker in the positive side protects only things on its loop or circuit. It should be in the only line that goes to the positive terminal of the battery. If you have more than one wire to the positive terminal, then the circuits on the other lines aren't protected.
My trailer came with a thermally reset breaker. It will trip in an overload (due to heat) and then when (and if) it cools off, it resets. This is handy because it's in an awkward spot to get to. But I have to keep in mind that it will reset and that the circuit can become "live" again suddenly. These are inexpensive, come in various amp ratings and are usually readily available in auto parts stores.