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Master shut off switch

P

plowhand

Member
Can a master shut off switch be put on the positive cable?..they recommend the negative but I've got some stray voltage and can't track it down.
 
In theory a master cut off is just like removing the battery from the unit. Even on the negative you should have no voltage leak as the battery is isolated. I have seen a few put on the hot side but for most applications it is always on the negative cable. Usually go to the unit and go to unhooking things one at a time, first being the alternator or generator. These late model units with computer controls is where it really gets harder to find. You did not state whet you were working on.
 
From you post im guessing you have it on the negative side. How could you have any stray voltage at all if it was cut off no matter what side the switch was on positive or negative. You must have a wire on the backside of the switch thats still in play before the cut off switch
 
Here's the problem I have it on the negative cable but when I have the master off I hit the start button and the solenoid clicks very low voltage not enough to engage starter..I checked the new master it does not ohm out in the off position.
 
Industry standard is on the ground. I was going to put mine on the positive side but my electric shop called and talked me out of it. I went with ground as Caterpillar is this way. They have more engineers working in electrical systems than about anybody else.
 
(quoted from post at 20:45:46 09/29/19) Here's the problem I have it on the negative cable but when I have the master off I hit the start button and the solenoid clicks very low voltage not enough to engage starter..I checked the new master it does not ohm out in the off position.
Click to expand...
tory does not check out. Remove the neg cable from battery post and tell us if nothing changes.
 
A bad cutout switch is dangerous (not at 12v, but who knows when it will conduct 100%). When you least expect it, your elected, Etc. Jim
 
What does "does not ohm out" mean? That is not a technical term or even a layman's term that means anything in common everyday language. Does the switch test as open circuit or some level of resistance?

If there are no other connections to the negative post on the battery (i.e. smaller wires jammed into the cable clamp, or connected to the clamp bolt), then the switch is faulty and is not disconnecting completely.
 
The switch needs to be connected directly to the battery post, through the switch, then to the grounds.

Having anything still connected to the battery defeats the purpose.
 
You need it on the cable between the battery and frame. The way you have it right now all your doing is isolating the starter. There are other things that ground through the frame in a different place. This is why the solenoid is working with the master shut off. Put it where I stated and the entire system will be dead when the ground is cut off at the battery circuit.
 
Assuming you are not running the tractor when "shutting it off", and assuming you are using a quality ohm meter, and assuming you are seeing an open circuit with the switch OFF, and assuming you are testing the switch with it disconnected at one end, there should be no possible way for the starter solenoid to make noise. What are you working on, it will help radically. Jim
 
O K I think you just explained it you need to move the switch to in between the battery and the ground. NOT between the ground and the starter. Or as JD seller tried to explain nothing between the switch and the battery post.
 
Jim working on a Moline G706.I can get a picture tomorrow of the set up.Ive been using a test light as well.I could try a new switch see what happens.
 
The neg side switch arc's less every time you close the contacts. The Pos side will arc and might eventually stop working sooner than the neg side. If you have any gassing of the battery and you arc a switch nearby, uh...oops? I have a fancy key operated switch on her Fergy and a simple knife switch on a Demonstrator.
 
Does the tractor have two sets of batteries??? If there is only one ground cable then your cut out switch is bad. They can fail by arcing inside. Just replace the cutout switch.
 
yes you can. I bought a naa tractor that the fellow who had it put a large handle shut off switch on it on the positive side. he did this so no one could try to start the tractor. his grand children kept turning it over with the push button switch.
 
I assume you're talking about one of those knife switches that attach directly to the battery post, as opposed to a switch you mount elsewhere. The reason for putting them on the negative cable is to prevent unintentional arcing should the switch touch the frame. Functionally they will work on either post, but just like you should always remove the negative cable first and install it last, it's safer to switch the ground.

That said, if you have a current draw that you want to stop, it doesn't matter which post it's on. Either way the switch takes the battery out of the circuit. So put it on the negative post unless it won't physically fit there.
 
Plowhand, To answer your specific question, YES it "could be" put on the positive cable, a battery disconnect switch still functions on EITHER post (Well DUH) its a simple DC series circuit and opening it stops current flow regardless of which post. Although a disconnect switch works, you need to locate the pesky problem, but you already know that, an ammeter and a VOM are tools which can help locate the problem. High resistance low current drains which eventually drain the battery can be a major pain lol. NOTE a simple 6/12 Volt DC test lamp may not be enough to locate the problem. There may not be enough current to light the lamp yet enough to eventually discharge a battery...??.

If the switch is "good" regardless of which battery post its on, in the Off/Open position there should be an open circuit (approaching infinity ohms on meters) through it, so I don't see how any electrical devices like a solenoid would receive any voltage whatsoever UNLESS there's an alternate current path elsewhere BUT THATS YOUR WHOLE PROBLEM which we cant locate over the net grrrrrrrrrrrrrr

John T
 
1)If either battery cable is completely disconnected from the tractor there is no way the electrical system on the tractor can run the battery down.2) I'd put the disconnect
on the negative side if its negative ground,but as a practical matter if there is no current draw there will be no arching on the positive side and will be very little arching if there is a small draw like a light bulb, it'd take a heck of a dead short somewhere to produce a big arch.3)Are you sure the battery isn't discharging while the tractor is running as in the charging system isn't working?
 
(quoted from post at 20:06:56 09/29/19) Industry standard is on the ground. I was going to put mine on the positive side but my electric shop called and talked me out of it. I went with ground as Caterpillar is this way. They have more engineers working in electrical systems than about anybody else.
Click to expand...

Not sure about industry standard, I've been around a number of older fire apparatus and logging equipment, all of them had master disconnects between the battery/batteries and the starter which was normally on the positive side.
Todays newer equipment many times have multiple wires connecting to the positive side and only one on the ground side so it's easier to install a disconnect on the ground side.

Either side will work as long as there's no other wiring connecting the that side of the battery.

On some equipment today the disconnect only interrupts the ignition system so that if one turns the key on nothing happens, this is done to maintain power to computers and radios that would other wise lose their memory.
 
Crazy Horse,
There is even a song about resistance, "Ohm, Ohm on the range where the deer and antilope play."
 
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