Lenie please don't feel bad. I go through this crap all the time! Latest project f-up was a fuel issue on my boat. Two fuel pumps, a fuel pump push rod, fuel log return valve and a redo of the tank pick up I finally replaced the non-ptfe return line. Dog fired right up.

Us non-pros learn a lesson each time we open the tool box. Fun huh? :)

^^^THIS^^^^

I'm failing to follow the logic of a couple posts here.
If I put my cutoff switch on the power side of the battery, it will absolutely see all the load that the vehicle is using. The power side, or positive side of the battery's circuit produces, or sees, the load. Lets say I'm using a cutoff switch rated for 50 amps, and my vehicle's electronics need more than the switch is rated for. The switch will eventually overheat and fail. Doesn't matter if you've rated the cables correctly, the switch will be the weak link. Ok, let's look at it from another view. Even if the switch is overrated for the vehicles load demands, and there is an accident that produces a short on the positive side of the battery, the switch will be the weak leak and fail. That's a good thing, as long sat the switch can be closed quickly, but what if it overheats and sticks closed, meaning you cannot open the switch? Not good. If the ground side of the circuit sees as much load as the power side, then why not fuse the grounds, and not the hot side? The ground side will see the voltage, but not the amperage, because the amperage is used by whatever is pulling it. You cannot push electricity. It has to be pulled.
So what if I place the switch on the negative side of the battery? First off, it does not see a load, and will never fail from overloading, and best of all if you remove the ground from the vehicle by switching the negative cable off, then there is never a chance of circuits becoming energized if the switch is off, meaning no "juice" can flow through them, because electricity has to have a ground, or you don't have electricity to start with. I've wired many race cars, and street cars, with cutoff switches, and believe me your taking an unnecessary risk by putting the master cutoff switch on the positive side. Will it work? Sure. Play it safe, and switch the negative side. No ground equals no power.
Did I tell you guys that I make a pretty good living messing with electricity?

Scott --- I told him that 15 posts ago..... HAHAHAHAHAHA



Once people actually UNDERSTAND electricity - it all makes more sense....



It's like a buddy of mine when I was trying to show him that he didn't need to run a ground wire from another ground wire and that the shortest path to ground was the best choice.... I still don't think he understood. It's only - he doesn't get the whole RELAY thing either! HAHAHAHAHAHA

Think of it like this ------



You have "hot" going all over the car to run many items.... but if they aren't seeing the ground side -- then they aren't hot! Real simple.



Take a battery cable -- run it to the hot side of the battery (12V +) -- never hook up the ground side of the battery.... run around with the 12V hot wire and touch all over the car - and you'll never have a spark. Why? Because there's no path to ground.

Yeah Greg, I follow you. Relays are fun. I've always said the easiest way to confuse a "smart" person is to throw a relay into the conversation.

Exactly!

But as a safety switch....i.e, you crash the car and need to shut it all off....isn't there a good chance you just created some new grounds when the car is all mangled?

That's what fuses are for. They blow, or trip depending on which style you use, if there is a short, from a possible wreck, or whatever, or there is overloading, meaning the current draw in the circuit is more than the fuse is rated for.

The beauty of putting the master cutoff in the negative side of the battery is that it can't fail from overloading, and when you turn it to off, there are no grounding points on the vehicle. No grounds equals no power. Anywhere.

If a vehicle is wired without fuses, it is a problem waiting to happen. I don't care if its a racecar with 3 circuits in the entire vehicle. Always use fuses.

If you connect the battery ground DIRECTLY too the switch only (maybe make sure the switch isolated too) then too frame...when you kill switch it will isolate everything part of that main circuit and its all parallel circuits(from - battery to load to +battery) because the circuit is incomplete so no power will flow... so even if u touch a power wire to a ground nothing will happen because no power is flowing with (switch off)..just make sure all circuits tap off main circuit... same idea as putting it the postive side but you would need switch rated to handle all the amps the car will need (including start up :welcome3: