Originally Posted by YC1
Resistance in series is resistance. Pure and simple. It does not matter where in line you put the resistance. The voltage drop will add up to the full potential.
Cat put shut off switches on the negative side of many heavy equipment pieces.
Electrically it does not matter.
In my reply, just before yours, I was going for sarcasm. Guess I failed. 38 years in the computer industry, much of it repairing mainframes. I did learn a little about electricity and electronics. Resistance in a circuit, at the positive end, the negative end or anywhere in between yields the same result. There are reasons to switch one end or the other, but not in this case. This is a simple 12v circuit.
Disconnect switches in most motorhomes disconnect the positive side. I'm sure that has to do with the layout, configuration of the wiring. Negative cables off the battery typically go directly to the chassis. Adding a disconnect would require extending the cables to the switch and back again. Positive leads already extend to various locations so it's easier to throw a disconnect in at a convenient location. You also don't want to switch the negative off the engine battery. Some switches can handle the current of a starter, some can't. Most motor homes switch the positive off the engine battery but that only disconnects power to the dash and other electronics. Power from the battery to the starter itself is usually a direct line with no disconnect.
Bottom line is you can break this simple 12v circuit anywhere you want before the breaker/fuse panel or between the frame and connection to the battery.