WARNING!!! Automotive Battery Disconnect Switches 

Thank you for posting this video, hopefully this saves people from injuring themselves! I have seen some Injuries from tools arcing across terminals mostly 24vdc and multiple batteries.

I was wundering about this since I putting one of these on my truck that only gets used once every few months I remember in shop class our teacher saying any car with a ecu never disconnect the positive terminal and if you do negative comes off first great video saved me a headache down the road

You sir are a gentlemen and a scholar, and there are few of us left.

In my youth, I once got a socket wrench across the positive 6 volt battery terminal and the rear seat frame of my 1956 Volkswagen. I can absolutely verify that a socket wrench will glow very red when shorted across a 6 Volt battery. The socket wrench welded itself to the seat frame and I had to kick it loose before the battery reached critical mass.

Finally someone posts a very useful warning! Good job!

Very informative video. I learned something new today about battery disconnect switches.

You confirmed what I suspected since the quick disconnect was apparently too small for the positive terminal of my top terminal battery. Thanks.

thank you never done this and had no details of how to so thank you very much for your info. now i can go forge ahead

You are 100% correct about the danger of creating a short from positive battery terminal to chassis ground. However, the safest method is to isolate the positive terminal with the battery disconnect switch, and then properly insulate the battery disconnect switch itself.

Please note how close the measurement tool gets to the positive terminal when measuring the negative post. Less than 1/4 inch before you've bridged the gap. Wow!!! Also the entire explanation of additional exposed metal toward the end of the video is correct, it adds risk, however not for the reasons you mention. It only adds risk if you contact that greater area with some part of the car that is positively charged, not bodywork, not other surface areas in the engine compartment, etc. These are all for the most part already grounded by the same cable coming off the negative post. There are virtually no exposed metal positive charged parts in a car except for the positive post of the battery. You are most risk of sparks and a short if you somehow bridge between the additional metal work and the positive battery terminal, as you almost did when using the measuring tool at the beginning of the video. You also forgot to mention how important it is to wear safety goggles whenever working with the battery in a car. There are many cases of blindness related to sparks coming from improperly jumped cars or other shorts when working with batteries.

Thanks for posting this! i just ordered one! lol

when I was 17, while installing a battery and connecting the positive connection I accidentally hit the fender with the wrench (yes, i had connected the negative already - my bad). That sucker gave one spark and blew the lid right off the battery. It was wintertime, and i had on a hooded grey sweatshirt. I got a small cut between the eyes from flying plastic and turned the hood of the sweatshirt bleach white. I got an ambulance ride but fortunately had no acid burns to my eyes. Lesson learned. I am still appropriately overcautious around batteries now.

Thanks for the ideas you have contributed here.

Nice video. A lot of useful information.

Much appreciate this video.

Did you see how close that guy came to melting his caliper (?) when showing the terminal diameters ? A very dangerous demonstration as one who has seen a shorted battery explode will testify.

Thanks for posting this. Caliper end was dangerously close. No mention that batteries can go BOOM from the explosive gasses?

Good video, thanks.

Very nicely done.

Thanks for this. I had no idea.

Thanks I did not know ,glad I watched

It all runs on smoke & once you let the smoke out, it doesn't work anymore. I always use a short extension on my ratchet when tightening the battery terminals to prevent doing just that. 3 cracked ribs from a battery box when I shorted out an 8D battery was enough of a learning curve!

great info

Thanks for the great video!

Thank you, I know now how to do it right.

Good tip

By installing battery kill switch, will it affect the engine management system?

Definitely reshoot the micrometer scene. I thought for sure we were going to see an explosion. Other than that GREAT INFORMATIVE VIDEO!

Are you "positive" about this??

very help full!!!!

Awesome POST

You are the MAN. hopefully all those "mechanics" are watching your videos thanks for your video.

I have an old Chevy Astro 89 I want to install a battery cut off switch to. I don't want a Frankenstein's power level and I dont want to have to open my hood to turn and twist a knob every time I'm ready to leave. I want to know if I can install an on and off switch, to the battery that mounts inside the car, I can flip to get the battery to make contact. There is some parasitic voltage leak that kills the battery within 1-2 weeks of non use and I cannot find where it's drawing from.

Wow you almost shorted the battery with your caliper and you are wearing a ring!!! woops!

Thank you

This video has lots of negative and positive feedbacks.

Great advice thank you! :)

That's what hammers and beer can metal is for.

SUPER INFORMATIVE AND NECESSARY VIDEO..THANK YOU

Can i use a lawn amd garden 220 cca natteey to crank my 1500 beetle engine? I like its smaller than most batteries

Can you suggest a product to use a replacement? Need a way to shut down anything that is powered by the battery from the ignition to the lights when out and away from the car. (not an alarm system).

You tricks good

Good Advice for the newbie and no-it-alls, you forgot to mention that the batteries have a bad habit of Exploding and really messing up everything including your life

You talk about leaving tools on the battery, what about the micrometer you used to almost connect the positive and negative?

I'm looking for quick connects that I can hook up a power inverter to my car battery. Do you have any recommendations? The cable I've built from the battery to the inverter is 3 gauge.

A like for you and wishing you a great weekend too.

Excellent - I am about to fit a 'Projecta" switch - BUT the salesman insisted it goes onto the Positive terminal. I queried this and pointed to the package saying "Suits negative battery post". He then said - oh well I suppose either post will isolate. I will speak to him..... However I do wish Projecta had made their instructions more forcefully by saying do NOT connect to positive.

You should be careful with your callipers. In this video they came very close to shorting your battery. Not a good example given your warning later with the ring spanner example.

by god I'll make it fit!

I have a battery drain that I cant find. I put one of these on my vehicle and the next day my vehicle battery was dead anyway. Anyone have any suggestions how I can create a kill switch that will work without removing both battery terminals every time I exit the vehicle? Thanks !

My generic group 35 battery has equal sized post and my switch sits on the positive side and nothing has happen but i have done all the above including a metal bar touching the battery to the chassie for some amazing sparking action lol.

That doesn't sound like a good enough reason to risk shorting out the terminals with any tool? Worse case scenarion the spanner or other tool would weld itself to the terminals and youd have to stand back and watch it burn itself out because getting hold of a red hot metal tool is NOT my idea of how to lose my fingers burning them to a crisp attempting to save a battery or tool. I wouldn't fancy cleaning up the mess afterwards either.

quick question,i just bough 2 T105RE 6 volt trojan golf cart batteries, hooked up in series for 12 volt system ,,,,first time i hooked them up to a 1.5 charger /maintainer they reached 13.6 before charge light turned green,,,,,,,a week later i hooked it up again but they reached 14.6 and still no green light,, i disconnected charger in fear of over charge,,,,,,,,,should i have allowed the charging process to continue to green light appeared ?........were the batteries attempting to equalize ?

I'm expecting no answer for this but a buddy of mine has a riding lawn mower that keeps draining the battery. Is a 12 volt toggle switch an option for killing a battery. I just don't know how a 4 or 6 or 8 gauge wire could mount to 2 tiny prongs and not burn up or something go wrong even on the Ground Side of the Battery.

In the end of this video you complain about 'so called mechanics' leaving their tools across the battery and how its dangerous and such. but at the 0:50 mark your dial calipers are about 1/2 away from hitting both posts

I found this information to be shocking.

I just wanted to see sparks

He kind of left out the main reason for a negative disconnect. All manufacturers and maintenance/repair manuals instruct you to disconnect the negative terminal before doing...whatever it is your going to do....

is this guy for real wow

I still do not understand why is this difference between ways to break the circuit. Positive, negative.... just break it, and it's all the same, or not?

I have a slow drain that is draining the battery over a course of a couple days. If I use the QD on the negative it'll still drain as there's a slow drain still due to the positive cable being hooked up making a circuit. I've got to disconnect the positive in order to break the connection. Thoughts?

You will disconnect power from your car's ECM and it will lose its settings no matter which terminal you disconnect.

I am confused - The April 14, 2014 post says "WARNING!!! NEVER connect your automotive battery disconnect switch to the POSITIVE terminal of your battery." One month ago you "Watch This" wrote "But I would have hoped that my video would have explained why breaking the POSITIVE side is preferable." ???

I have a kill switch on my car that worked great on my positive terminal. Then all of a sudden one morning I turn the key to start it the switch keeps wanting to turn off all the power to the car. It doesn't stop doing this. What might this be?

gracias but you messed it up with the second advice. duhhhh

A friend once decided to short the terminals on a 12 v battery to see if it was fully charged/ functional. It welded the screwdriver to the terminals and then the battery exploded destroying the building.

im guilty of the tools on the battery.. yikes..

Who the hell puts tools on top of the battery?

There's another reason why a switch is more practical on the negative terminal: The positive corrodes far quicker, which can be prevented by covering both terminal & cable with acid free vaseline. If the switch is placed on the positive terminal, you pretty much end up greasing the entire assembly... There's no need to grease up the negative terminal.

Who the hell has got so much room in their battery compartment for all these dumb disconnect switches anyway? And around batteries use insulated tools and or have a insulating cap and cover on one terminal!

well then just install the fucking thing on the negative post problems solved

why are you talking so robotic I think you have watched 1 to many 50's and 60's videos lol

DON'T tell me what to do

remember power go's from neg to pos that is why you always take off the neg wire, look in you auto books read !!!!

Thanks for the tips safety sam ( sarcasm)

At 3:15 a warning is given about tools on battery and I agree that's bad that's why I'm all for laws that increase safety, will you help me pass a law that has everyone in a car wear a motorcycle helmet as well as reinforced caging inside the cab...thank you ....

why am i here is this not common sense. Rule #1 if you don't know what you are doing leave it alone .. just joking we all learn my our mistakes

Why put a disconnect on a vehicle unless it is for off road use? Buy a cheap tool set and just pull the cables off! And there are POSITIVE disconnects they are designed in a different manner and do not connect directly at the battery post.