# Criss-crossing jumper cables: What would happen? **URL:** \ **Category:** Factual Questions\ **Created:** [February 6, 2015, 6:16pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990 "2015-02-06T18:16:35Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [February 6, 2015, 6:16pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/1 "2015-02-06T18:16:35Z")
And, just in case you’re wondering, no, I don’t. Anyway, if I connected my jumper cables to unlike poles, other than possibly melting my cables, would damage be done to the batteries themselves or the electrical system? If I cranked up the ‘live’ vehicle in this situation, would that mess things up? ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [February 6, 2015, 6:21pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/2 "2015-02-06T18:21:04Z")
the batteries could be damaged by the high current flow. depends on your vehicle, age and type, the electrical system could have parts destroyed. you will melt your cables, not totally but the clamps will have damage. ---
**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:** [February 6, 2015, 6:22pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/3 "2015-02-06T18:22:37Z")
> [@Earl\_Snake-Hips\_Tucker](#): > > And, just in case you’re wondering, no, I don’t. > > Anyway, if I connected my jumper cables to unlike poles, other than possibly melting my cables, would damage be done to the batteries themselves or the electrical system? Yes & Yes > > If I cranked up the ‘live’ vehicle in this situation, would that mess things up? Yes. I doubt you could unless you already had it started. :smack::smack::eek::eek: IMO answers are those in red. ---
**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:** [February 6, 2015, 6:32pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/4 "2015-02-06T18:32:36Z")
It’s possible to fry various control modules (“computers”) which cost hundreds of dollars each. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [February 6, 2015, 7:04pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/5 "2015-02-06T19:04:49Z")
I’ve seen this done on an old Beetle where the wires to the battery were the wrong color (ground was red and +12 was black). The wires and clamps got hot but didn’t melt. The radio was fried, but nothing else was damaged. An old Beetle’s electrical system is extremely simple, and is pretty rugged due to its simplicity. I would expect a modern car’s various computers to be fried. It’s also possible that the battery electrolyte can boil from the excessive current and the battery can explode. If left in place for any length of time, the batteries can easily be discharged to the point where they chemically self destruct. Lead-acid batteries don’t like to be completely discharged. ---
**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:** [February 6, 2015, 7:10pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/6 "2015-02-06T19:10:39Z")
Bad, bad things, possibly to both vehicles and whoever’s nearby. I have more than once been bitten by cars with wrong-colored battery cables (and may whoever picked up the cheaper one at NAPA, assuming “they’d remember” or didn’t care, roast in the deepest pit of hell). It’s NOT fun, even when no permanent damage results (probably because you grabbed the red-hot cable or clip and yanked it free in time). ---
**Author:** ![awldune](https://avatars.discourse-cdn.com/v4/letter/a/c77e96/32.png) [@awldune](https://boards.straightdope.com/u/awldune)\ **Post date:** [February 6, 2015, 7:55pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/7 "2015-02-06T19:55:50Z")
> [@Gary\_T](#): > > It’s possible to fry various control modules (“computers”) which cost hundreds of dollars each. I can attest to this ☹ ECU and several relays and IIRC the alternator. What I did was to install the battery backwards (really, the wrong battery) rather than a jumper mishap, however. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [February 6, 2015, 8:15pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/8 "2015-02-06T20:15:29Z")
DON’T CROSS THE CABLES! It would be bad. Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light. Total [del]protonic[/del] electronic reversal! ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [February 6, 2015, 8:29pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/9 "2015-02-06T20:29:07Z")
> [@johnpost](#): > > the batteries could be damaged by the high current flow. > > depends on your vehicle, age and type, the electrical system could have parts destroyed. > > you will melt your cables, not totally but the clamps will have damage. I witnessed the results of crossed cables, and the cables did indeed melt. Not entirely I’m sure, but enough to break the flow. This is 20-30 years ago, so perhaps there are better safeguards or other changes in design by now. ---
**Author:** ![Mr.Duality](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mr.duality/32/4098_2.png) [@Mr.Duality](https://boards.straightdope.com/u/Mr.Duality)\ **Post date:** [February 6, 2015, 9:19pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/10 "2015-02-06T21:19:53Z")
> [@Gary\_T](#): > > It’s possible to fry various control modules (“computers”) which cost hundreds of dollars each. Been there, did that. It was 30 years ago so better safeguards may be designed into modern cars, but I doubt it. ---
**Author:** ![justmeetee](https://avatars.discourse-cdn.com/v4/letter/j/898d66/32.png) [@justmeetee](https://boards.straightdope.com/u/justmeetee)\ **Post date:** [February 7, 2015, 2:17am UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/11 "2015-02-07T02:17:04Z")
I was standing behind a friend one evening in 1994 when he crossed a pair when putting the clamps on the running car. Took about five seconds before that battery blew up and a piece of the casing ripped through his left eye. Since then I double, triple and fourple check. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [February 7, 2015, 10:04am UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/12 "2015-02-07T10:04:06Z")
> [@justmeetee](#): > > I was standing behind a friend one evening in 1994 when he crossed a pair when putting the clamps on the running car. Took about five seconds before that battery blew up and a piece of the casing ripped through his left eye. Since then I double, triple and fourple check. I dunno if it would help, but I’m not comfortable doing that without the safety glasses, and I always turn side-on to protect my gonads. ---
**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:** [February 7, 2015, 1:14pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/13 "2015-02-07T13:14:37Z")
> [@Mr.Duality](#): > > Been there, did that. It was 30 years ago so better safeguards may be designed into modern cars, but I doubt it. modern ECUs have reverse battery protection built in, but it’s a one-time deal. Basically there’s a diode across the B+ supply pins, and if you connect power to the ECU in reverse the diode will make the input look like a dead short and blow the fuse for that circuit. ---
**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:** [February 7, 2015, 9:04pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/14 "2015-02-07T21:04:38Z")
> [@engineer\_comp\_geek](#): > > I’ve seen this done on an old Beetle where the wires to the battery were the wrong color (ground was red and +12 was black). The wires and clamps got hot but didn’t melt. The radio was fried, but nothing else was damaged. They may not have been the ‘wrong’ color cables. There were old Beetles that were actually made with positive ground systems. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [February 7, 2015, 9:35pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/15 "2015-02-07T21:35:39Z")
> [@Hail\_Ants](#): > > They may not have been the ‘wrong’ color cables. There were old Beetles that were actually made with positive ground systems. Early VW’s were 6 volt, but I don’t think they were ever positive ground. That was almost entirely a British thing. Beetles used a body ground so the negative cable would have originally just been a big honkin’ braided metal ground strap. They did tend to deteriorate, so I’m guessing a previous owner of **engineer\_comp\_geek** ’s bug replaced it with a generic battery cable, although I probably wouldn’t have chosen a red one given that the positive cable is black. (The red=positive black=negative cable convention wasn’t all that common on older foreign cars.) ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [February 7, 2015, 10:47pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/16 "2015-02-07T22:47:57Z")
> [@GreasyJack](#): > > Early VW’s were 6 volt, but I don’t think they were ever positive ground. Positive ground until the mid '60s, maybe until they turned 12V around '67. But it was not uncommon to convert the whole thing to 12V negative ground when doing a rebuild. Also, in the German standard wiring system (DIN), Red was “unswitched battery connection”, so certainly after the fuse box all the negative wires would have been red: I’ve never seen an old car with original wiring but I would expect the negative terminal lead to be red also. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [February 7, 2015, 11:16pm UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/17 "2015-02-07T23:16:26Z")
> [@Melbourne](#): > > Positive ground until the mid '60s, maybe until they turned 12V around '67. But it was not uncommon to convert the whole thing to 12V negative ground when doing a rebuild. Do you have a cite on that? I’m almost positive (:)) they were negative ground from the start and googling the only references to them being positive ground seem to be from people who think 6 volt and positive ground always go together. And yeah, once they got to the fusebox red= unswitched hot and black = switched hot but usually the positive battery cable was just a big beefy black wire. Sometimes the smaller wire that actually went to the fusebox was red, but not always. ---
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [February 8, 2015, 8:14am UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/18 "2015-02-08T08:14:00Z")
> [@GreasyJack](#): > > Do you have a cite on that? I’m almost positive (:)) they were negative ground from the start and googling the only references to them being positive ground seem to be from people who think 6 volt and positive ground always go together. > > And yeah, once they got to the fusebox red= unswitched hot and black = switched hot but usually the positive battery cable was just a big beefy black wire. Sometimes the smaller wire that actually went to the fusebox was red, but not always. I have owned over 25 VWs built from 1955 to 1966, all six volt, and NONE were positive ground. I have just checked two of my VW maintenance manuals. Both manuals state that the electrical system is six volt negative ground. I believe they were all negative ground. Like GreasyJack said “Early VW’s were 6 volt, but I don’t think they were ever positive ground. That was almost entirely a British thing.” Note the almost. Some early US built trucks & tractors were positive ground. For example the 1945 ish Caterpillar D-2 was six volt positive ground. Safety tip: When jump starting an early D-2 with a six volt VW, do not let the door to the VW touch the tracks on the D-2. AMHIK! ---
**Author:** ![russian\_heel](https://avatars.discourse-cdn.com/v4/letter/r/f05b48/32.png) [@russian\_heel](https://boards.straightdope.com/u/russian_heel)\ **Post date:** [February 8, 2015, 8:38am UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/19 "2015-02-08T08:38:12Z")
24 years ago, as a well meaning soul I offered to jump start a fellow employees disabled car. I had ZERO clue what I was doing, all I remember are sparks and smoke coming off her battery where the cables met. I said sorry, can’t help you, she called her husband, and I high tailed it out of there! Today I know better, but if you don’t know exactly what you are doing with jumper cables, better off not using them and calling a mechanic or AAA. Electricity is not something to fuck with. ---
**Author:** ![Deereman](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@Deereman](https://boards.straightdope.com/u/Deereman)\ **Post date:** [February 8, 2015, 9:32am UTC](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990/20 "2015-02-08T09:32:48Z")
On the positive ground issue, it doesn’t matter whether a car is positive or negative ground. The battery is the same as any other battery, hook it up positive to positive and negative to negative. Just do NOT let the vehicles touch, I’m not exactly sure what’d happen, but it would be very bad. [Next page](https://boards.straightdope.com/t/criss-crossing-jumper-cables-what-would-happen/711990.md?page=2)