Battery cut-out switch polarity

[HDowse]

I'm going to install a battery cut-out switch sometime soon and would like to interrupt the positive ground rather than the hot side because it looks easier to do. Electrically, I can't see any reason not to do so but would like to hear what others think.
I installed my carburetor that CharlieNY rebuilt along with a rebuilt fuel pump and distributor from him. The work he did is top notch and the car starts on one compression when warm.

[JSeery]

Some people get all worked up over this, but I don't see a problem with it at all. Just keep in mind that it does not totally isolate the battery because if something happened to short the terminal of the battery to the frame (or any metal) it would could still spark and arc! Again I think it is a remote possibility and it wouldn't bother me to do it like you are suggesting.

[john in illinois]

JS wouldn't disconnecting the positive ground wire isolate the battery from the frame?

John

[JSeery]

Originally Posted by john in illinois

JS wouldn't disconnecting the positive ground wire isolate the battery from the frame?

John

Yes, that is why I would use it.

[chap52]

Just remember that the majority of electrical issues with our vehicles are "ground" related. Remember this cut-out down the road if a problem arises.
I have a folder full of my truck receipts with "reminders" scribbled all over the front of it.
Besides it will provide hours of adventure for the next owner as they try to decode the notes.

[koates]

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Yes that is the way to do it by isolating the ground cable from the battery. Does not matter if battery is Neg or Pos to ground. If you do it that way and are then working on the car and accidently touch a wrench or screwdriver on to a terminal that is normally powered and to a ground you will not get a big spark or short. If you isolate the main battery power cable with a switch, then there is still a voltage potential on the battery power or hot terminal and any other cables connected there (if any). I have all my cars isolated in the ground cable and have done it this way for 50 years. Some racing bodies require the hot cable to be isolated but this does not make it safer in my book. Regards, Kevin.

[Fordestes]

After nearly 50 years in the trucking industry , I vote for using the ground as the switch point ,after all no ground, nothing can short , If the switch or for some reason the disconnect is bypassed as a rule the system will be as a normal operative system , if the non ground side is disconnected the system power can be available to short to the frame and the switch will be useless . I have used a lot of different brands , as of late I use the cole Hersee brand capable of a bout a thousand amps . from a truck supply , I don't have a mod. number handy its in the 25.00 to 35.00 range compared to the good but expensive priced units, I buy a lot from Truck pro and Fleet pride. These disconnects have lasted many years on high ampere earth moving equipment.

[my4dv8]

Did just the same thing on our 49 coupe. Put a cut off on the ground terminal . Just had to run a seperate ground wire to the late model stereo for a constant feed. Feel there is lees risk using the ground lead and a good quality switch.

[HDowse]

All great answers and that's the way I will go. The guys at my local Model A club think the same way, too. Fordbarn is like having a live technical manual at your fingertips, especially for a V8 newbie like me....

[Ross F-1]

Originally Posted by my4dv8

Did just the same thing on our 49 coupe. Put a cut off on the ground terminal . Just had to run a seperate ground wire to the late model stereo for a constant feed. Feel there is lees risk using the ground lead and a good quality switch.

Unless the stereo is not grounded to the chassis by its mounting screws, that arrangement will result in a "hot" condition even with the disconnect disconnected.

[flatheadmurre]

On trucks having clocks, stereo and other stuff needing constant feed the disconnect switch is always in power feed not the ground.
And the constant feed should be fused near the battery feed.
It was common to break the ground way back nowdays all switches factory installed is in the power feed, this is on neg ground both light an heavy equipment.
Must be a reason all manufacturer went this route.

[Chisel]

Take it for what it's worth. Tip 37 in the Ron Francis Wiring Catalog issue #43 page 104.

[koates]

Chisel, Yes the above tips from Ron Francis are correct for a modern car with electronics. The original question was old car related (1940 Ford) and I still prefer battery ground cable switching for those early model cars. Regards. Kevin.

[russcc]

I always switch the ground off, (old cars), and use the Cole Hersee switch. It is no longer made in the USA, Boston, MA, where Cole Hersee is located, but in Mexico. If you do an internet search like Google you usually find it for about $28. including shipping from truck suppliers as suggested. It's the best there is.

[36coupe]

When ever I travel with work, which isn't the case anymore I take 1/2" wrench and remove the ground cable. And leave the wrench on the battery until I hook it back up the next time home.

[Fordestes]

There is a disconnect for computerized or stereo clocks to keep power as the disconnect is turned off, It has a separate small terminal for this purpose.
Fordestes

[40cpe]

A ratcheting relay is convenient to operate without going under the hood. Just run a toggle switch inside the car.

http://www.amazon.com/Intellitec-Bat...connect+switch

[Chisel]

Originally Posted by flatheadmurre

It was common to break the ground way back nowdays all switches factory installed is in the power feed, this is on neg ground both light an heavy equipment.
Must be a reason all manufacturer went this route.

This was not to start an argument, but to point out what Ron Francis Wiring recommends to protect your instruments and to help answer flatheadmurre question.

[Drbrown]

Like russcc, I use a high-amp rated Cole Hersee disconnect switch after getting tired of the thumb-knob disconnect that was on the battery, and having to constantly open and close the hood. The on-off rotary switch knob is located inside next to the the heated box, inconspicuous but within reach of the driver.

My modified '47 came to me with 12v negative ground system and alternator. I use the four-terminal disconnect switch, which also disconnects my alternator, on the positive side of the batt. Considering the modified state of my car, and to reduce electrical hazards, I also choose to use vinyl cap-covers on my battery and solenoid terminals.

[MGG]

Originally Posted by Chisel

Take it for what it's worth. Tip 37 in the Ron Francis Wiring Catalog issue #43 page 104.

Possible dumb question - How can a short anywhere do damage if the circuit is broken by a switch at either the hot or grounded battery terminal?