What happens if you hook up jumper cables backwards on a car?

People say you just blow a fuse, some people say you can fry the computer other people say you need a whole new electrical harness... Who's right???

7 Answers

Relevance
  • 1 decade ago
    Best Answer

    Actually they are all correct and then some. A lot depends on the quality of jumper cables that you use. It is not a good thing and if you insist on trying it take two older batteries you can actually get some used ones at the junk yard and do this. be prepared for a large spark and possibly a battery exploding.so where some protective equipment.

    If the battery doesn't blow it will eventually fry the battery cables.. Electricity is weird and it usually never does the same thing twice. You will find that elec power will follow the path of least resistance. That is why one person said it will do one thing and someone else said something different. They have experienced it differently. I have

    seen a multitude of things that have happened to people when the jump a car not knowing how to do it correctly.

    Source(s): Master Mechanic shop owner 40 yrs
  • Anonymous
    4 years ago

    Check all the other fuses and fuse links - look especially for one that is in the circuit to the computer. It isn't likely you hurt your starter unless it was engaged when you did the deed, but you may have fried the starter solenoid. If it is accessible, and you have a 12 volt tester, you can test it by touching the tester to the starter terminal and to a ground while you try to start the car. If the tester shows current flow the starter may have been affected. If no current, replace the starter solenoid - they aren't too expensive. If you have checked everything mentioned without finding a problem, it is most likely the computer. If you know where it is located in the car you can pull it out. Before I thought about buying a new one I'd ask at Auto Zone, or some other parts store, if it was testable. If not I'd start calling the auto salvage places to find a good used one. Don't know what it would cost, but buying a new one will likely cost a pretty penny. Good luck. Note: even with a dead alternator the new battery should have power to operate the starter. Further note: don't know about yours, but some solenoids are actually on the starter. if that's your case, take the starter off and have it tested.

  • Anonymous
    1 decade ago

    Well first of all if you hook up jumper cables backwards you will get a big spark off the battery. telling you it is something wrong. and you need to check your connections. For this not to happen look at your battery before hooking up the cables. There it a + for positive which is red and a - for negative which is black. But the only real damage is maybe a blown fuse . and it dose not happen all the time

  • 1 decade ago

    lets just say nothing good. Your chips may get fried before any fuse has a chance to kick in. This goes for BOTH cars in the boost.

  • How do you think about the answers? You can sign in to vote the answer.
  • 1 decade ago

    you can kill the cells on both bat's u can fry both computers. you cannot fry the wiring harness unless your hooking it up to the hover dam backwards.

  • 1 decade ago

    Sparks -BANG!

    maybe you will get away with no damage and just burn out your jumper cables is not something I want to try!

  • 1 decade ago

    first of all the battery could explode.

Still have questions? Get your answers by asking now.