# Disconecting the negative terminal **URL:** \ **Category:** Factual Questions\ **Created:** [March 19, 2013, 5:40pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373 "2013-03-19T17:40:02Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Mdcastle](https://avatars.discourse-cdn.com/v4/letter/m/958977/32.png) [@Mdcastle](https://boards.straightdope.com/u/Mdcastle)\ **Post date:** [March 19, 2013, 5:40pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/1 "2013-03-19T17:40:02Z")
There’s this warning: “disconnect the negative terminal of your car battery before any work or the airbags will explode in your face and you will die” Has this actually happened? Is the airbag to dumb to not differentiate between driving into a semi vs trying to fix the heated seat or changing the ash tray bulb? As common as it is to work on a car, why not have a main disconnect for the car, and a battery backup for the radio? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 19, 2013, 5:54pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/2 "2013-03-19T17:54:39Z")
A lawyer did it. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [March 19, 2013, 5:55pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/3 "2013-03-19T17:55:35Z")
> [@](#): > > Has this actually happened? Is the airbag to dumb to not differentiate between driving into a semi vs trying to fix the heated seat or changing the ash tray bulb? the airbag inflator is simply a small coil of wire embedded in the propellant. any significant current through that wire can heat that wire coil and deploy the bag. The airbag/inflator doesn’t know whether that current came from the RCM or someone accidentally shorting to one of its terminals. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [March 19, 2013, 6:00pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/4 "2013-03-19T18:00:28Z")
Just a warning label to try & cut down liability also a last ditch effort to get folks to not do it wrong & make things worst. Airbags are like loaded guns, not smart to mess around with therm … Heck, the whole car is dangerous. Main disconnect = removing the negative terminal. Lost cheaper that a special gizmo… Never discharged an airbag while messing with wiring, but I bet someone somewhere has managed to do it so warning labels it is. ---
**Author:** ![dolphinboy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dolphinboy/32/330_2.png) [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)\ **Post date:** [March 19, 2013, 6:04pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/5 "2013-03-19T18:04:17Z")
It may just be the potential for a lawsuit and not based on it ever happening. I’m sure it’s someones job at a car company to come up with warnings as a way to reduce their liability, if only by a small amount. I’ve got warning stickers all over my new Toyota… doesn’t mean I have read any of them though… ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [March 19, 2013, 6:06pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/6 "2013-03-19T18:06:14Z")
Also, it is the negative terminal because it is easy to short the wrench to ground when loosening the terminal, and that will/may cause big sparks/hot melty stuff/exploding battery if you are doing the positive one, but nothing at all if it is the negative. Once the negative is off, it is then safe to work on the positive unless the vehicle has multiple batteries,(Diesels, jumpy low-riders, kidney massaging stereo equipped customs) then you need to take all the negatives off before touching any of the positives. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [March 19, 2013, 6:09pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/7 "2013-03-19T18:09:59Z")
Never touch any electrical component of a car without disconnecting the ground first. At best, you won’t have to replace pointlessly blown fuses. At worst, you won’t burn off your ring finger or set fire to the car. It’s not a lawyer thing, it’s a don’t-be-fucking-stupid thing. ---
**Author:** ![Mdcastle](https://avatars.discourse-cdn.com/v4/letter/m/958977/32.png) [@Mdcastle](https://boards.straightdope.com/u/Mdcastle)\ **Post date:** [March 19, 2013, 6:19pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/8 "2013-03-19T18:19:50Z")
Well, would it be save to unbolt the seat or change a light bulb if the switch was off with the battery connected if I’m not touching any live wires? The seat needs power to slide back and forth to get at the bolts. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [March 19, 2013, 6:41pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/9 "2013-03-19T18:41:42Z")
Good question… I wouldn’t disconnect the battery just to change a light bulb, but if your seat has side-impact airbags (normally, this is identified with an “AIRBAG” tag sewn into the seam) all bets are off. If you’ve got [airbags in the seats](http://www.proseatcovers.com/help/airbags), investing in a shop manual for the car might be prudent. It’s probably OK to move the seat back and forth to access the bolts, but then you’d need to determine the proper procedure for disconnecting the airbags. I think the days where you could set off the steering wheel airbag just by smacking a sensor are behind us, but you can still set them off with an accidental short circuit or some othe accidental “perfect storm” event that makes the car’s computer think “Crash!” ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [March 20, 2013, 3:06am UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/10 "2013-03-20T03:06:46Z")
All airbag wiring is usually wrapped in day-glow yellow casing so as not to be messed with by any mechanic, amateur or pro alike. While it’s highly unlikely that you’d ever set one off, it’s far from impossible if you don’t disconnect the battery. All you’d have to do was stick a live continuity or other hot 12V probe into the right (or wrong!) one of its wires, and _ **KA-BLAMMO!** _ It’s a bit of an exaggeration, but remember TWA Flight 800? Conspiracy nuts aside, that’s essentially what happened to it, a short circuit back-fed high voltage into a low voltage fuel tank sensor. Very bad day… ---
**Author:** ![JBDivmstr](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@JBDivmstr](https://boards.straightdope.com/u/JBDivmstr)\ **Post date:** [March 20, 2013, 6:29am UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/11 "2013-03-20T06:29:05Z")
_ **This** _ [Blague de mécaniciens (explosion d'un airbag) - YouTube](http://www.youtube.com/watch?v=EoHGR4QMdcw) is an excellent example of just how powerful auto airbags are. :eek: ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 20, 2013, 9:44am UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/12 "2013-03-20T09:44:48Z")
> [@JBDivmstr](#): > > _ **This** _ [http://www.youtube.com/watch?v=EoHGR4QMdcw](http://www.youtube.com/watch?v=EoHGR4QMdcw) is an excellent example of just how powerful auto airbags are. :eek: What’s “Hey guys, watch this!” in French? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [March 20, 2013, 11:57am UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/13 "2013-03-20T11:57:43Z")
> [@beowulff](#): > > What’s “Hey guys, watch this!” in French? What’s “help, I have multiple compression fractures of the spine” in French? I’m envisioning a lifetime of chronic back pain for anyone like this guy who sits on an airbag while it fires. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [March 20, 2013, 1:34pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/14 "2013-03-20T13:34:18Z")
> [@gotpasswords](#): > > I wouldn’t disconnect the battery just to change a light bulb… I suppose there’s a level of electrical service or repair below which the need to disconnect the battery would be unnecessary, but having blown fuses while changing minor light bulbs, I will usually do it for anything involving wires. It’s one of those cases where the minute or two of time invested helps insure against multiplying the duration and difficulty of the job greatly. ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [March 20, 2013, 1:38pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/15 "2013-03-20T13:38:28Z")
> [@Machine\_Elf](#): > > What’s “help, I have multiple compression fractures of the spine” in French? I’m envisioning a lifetime of chronic back pain for anyone like this guy who sits on an airbag while it fires. I’m imagining him punching the assholes who did that. That was pretty messed up. And yes, could have resulted in injury. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [March 20, 2013, 1:48pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/16 "2013-03-20T13:48:36Z")
> [@NitroPress](#): > > I suppose there’s a level of electrical service or repair below which the need to disconnect the battery would be unnecessary, but having blown fuses while changing minor light bulbs, I will usually do it for anything involving wires. Disconnecting the battery is overkill for this. Don’t turn the circuit on and you can’t blow a fuse. Simple. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [March 20, 2013, 1:53pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/17 "2013-03-20T13:53:57Z")
> [@echo7tango](#): > > I’m imagining him punching the assholes who did that. 😕 Why? He appeared to be complicit in the stunt. ---
**Author:** ![wedgehed](https://avatars.discourse-cdn.com/v4/letter/w/8edcca/32.png) [@wedgehed](https://boards.straightdope.com/u/wedgehed)\ **Post date:** [March 20, 2013, 1:56pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/18 "2013-03-20T13:56:55Z")
Reminds me of Air Force horror stories about setting off an ejector seat inside a hangar. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [March 20, 2013, 2:05pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/19 "2013-03-20T14:05:07Z")
> [@Gary\_T](#): > > Disconnecting the battery is overkill for this. Don’t turn the circuit on and you can’t blow a fuse. Simple. Many circuits in modern cars are hot all the time, and the ones that aren’t are adjacent to ones that are. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [March 20, 2013, 2:11pm UTC](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373/20 "2013-03-20T14:11:10Z")
a windshield repair place has on the aftercare instructions that they disconnect the battery before doing work and you may need to reset some electronics. [Next page](https://boards.straightdope.com/t/disconecting-the-negative-terminal/653373.md?page=2)