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Battery Disconnect , Positive or Negative ??

Discussion in 'The Hokey Ass Message Board' started by Bob 1743, Sep 27, 2007.

  1. buffaloracer
    Joined: Aug 22, 2004
    Posts: 816

    buffaloracer
    Member
    from kansas

    NHRA says positive. My electrical engineer friend says negative. He uses Larry's line "you can't fix stupid".
    Pete
     
  2. Fortunateson
    Joined: Apr 30, 2012
    Posts: 5,331

    Fortunateson
    Member

    Buy two and attach one to pos and the other to neg.

    Edit: as others have said earlier.
     
    Last edited: Mar 2, 2018
    clem likes this.
  3. denis4x4
    Joined: Apr 23, 2005
    Posts: 4,198

    denis4x4
    ALLIANCE MEMBER
    from Colorado

    Three cars and two boats all have negative disconnects
     
  4. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    That is what I was taught 50 something years ago. Disconnect the ground side first. For racing + side may be a feel good thing but for the car in the garage disconnecting the ground shuts everything off plus if something gets dropped on the + post and goes to bare metal there is no chance of it shorting out. You have the battery grounded there is that chance of something shorting out on the + post. Slim but still a chance. As far as presets, I just pulled the dead battery out of one of my OT rigs yesterday after it sat for a year. Put the new battery in this morning after the old one spent the night at the tire store and flunked it's test this morning. Stuck the new battery in, electronic items in the car made noises and quieted down. Fired it up and my preset go to station came on. Now if the over heating problem miraculously healed it's self life is good.
     
  5. Dirk35
    Joined: Mar 8, 2001
    Posts: 2,067

    Dirk35
    Member

    I have mine on the Positive side. Its mounted on the firewall and I reach under the dash to turn it on/off. That makes the back of the posts for it accessible for the battery tender and for anytime I need to jump start the car because my battery is under the car and difficult to get to.
     
  6. caton462
    Joined: Jul 17, 2013
    Posts: 176

    caton462
    Member

  7. caton462
    Joined: Jul 17, 2013
    Posts: 176

    caton462
    Member

    The schematic in my last post is how I use the + side for NHRA, keeps the alternator from powering the engine. Make sure you use a switch heavy enough wherever it is installed.
     
    juan motime likes this.
  8. mike bowling
    Joined: Jan 1, 2013
    Posts: 3,560

    mike bowling
    Member

    If you,re just talking about storage, I usually take my battery out. Then throw it on a trickle charger for a day or two when you're ready to put it back in. I also pull the positive terminal off in between times if the car is going to sit and not be driven for days or even weeks( hopefully not often). Fire freaks me out!


    Sent from my iPad using H.A.M.B.
     
  9. I do Positive as close to battery as possible. My reason is that is the way I do it!o_O
     
    325w likes this.
  10. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,552

    Cosmo49
    Member

    Positive, as it was convenient.
     
  11. Kevin.Morrison
    Joined: Jul 17, 2018
    Posts: 1

    Kevin.Morrison

    Good afternoon everyone... I am having an issue with my truck and I am hoping that this is the place to find an answer.
    My truck is a 2002 Ford Ranger XLT, extended cab, 3.0L, v6, 2wheel drive

    My radio, wipers and windows stopped working... apparently, the master control module messed up and I don't have the money to get a new one from the dealer and have them flash it to my truck's VIN. roughly $800. O__O

    Anyway, I have a bypass running to the battery, a fuse with popper just in case, and I just ordered a Blade Disconnect.

    Now, my bypass is running, obviously to the Positive terminal. The Disconnect says it is for the Negative Terminal, but I'm worried about battery drain with the wire constantly on the Positive Terminal. Can I use the Disconnect on the Positive Terminal instead or will I encounter a problem?

    Thank you all for your time.
     
  12. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 12,287

    Bandit Billy
    ALLIANCE MEMBER

    The switch likely doesn't know which terminal it is connected to. Make sure you fix your problem and don't rely on the Band-Aid.

    Oh, and since this thread popped back up I will weigh in. I connected to the positive cables using this switch.
    upload_2018-7-17_14-45-42.png
    It will stop a running motor and kill everything on the car. Will yours?
     
    juan motime likes this.
  13. Ralphies54
    Joined: Dec 18, 2009
    Posts: 772

    Ralphies54
    Member

    If the ground is disconnected how can any "upstream short' get back to the battery negative to complete the circuit. Even an 'Earth' ground wouldn't work because of the rubber tires!! Ralphie
     
    Blues4U likes this.
  14. Is anyone positive that it's negative ? :cool:
     
    LAROKE and leadfootloon like this.
  15. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 12,287

    Bandit Billy
    ALLIANCE MEMBER

    Yes, but I'm bipolar.
     
    LAROKE and milwscruffy like this.
  16. XXL__
    Joined: Dec 28, 2009
    Posts: 2,117

    XXL__
    Member

    Hot side. Ground is something that can pop up in a number of places. By disconnecting ground, you give the circuit the chance to find those other sources (through that ground strap you forgot you had, through the antenna shielding, through door pin switches, and so,on... BTW, many of these grounds are insufficient, so you may also get fire thanks to too much current getting drawn through them). I have high confidence (though nothing official to support) that is why NHRA would require it on the hot side.

    /2 cents

    Edit: oops... @Jalopy Joker and others have touched on this point in the middle of the thread.
     
    Bandit Billy likes this.
  17. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 12,287

    Bandit Billy
    ALLIANCE MEMBER

    And, per NHRA, the switch has to kill the running motor in case of a mishap when the battery is located in the trunk. If you eliminate the ground the motor will still run. You must kill the power to the fuse box and the power from the alternator.

    If you try that with a 2 post cut off switch in which the alt cable and the acc cable share the same lug on the kill switch, the alternator feed will route back to the fuse box and the motor will run on. All that was accomplished was to isolate the battery in this case.

    You need 4 posts on the kill switch to isolate both alternator and accessory circuits from each other and from the battery.
     
    XXL__ likes this.
  18. davidvillajr
    Joined: Apr 4, 2005
    Posts: 1,165

    davidvillajr
    Member

    Might it just be a question of grammar/synonyms rather than specific + or - instruction?

    Positive:
    2. with no possibility of doubt; clear and definite.
    synonyms: definite, conclusive, certain, categorical, unequivocal, incontrovertible, indisputable, undeniable, unmistakable, irrefutable, reliable, concrete, tangible, clear-cut, explicit, firm, decisive, real, actual
    "positive proof"

    I don't know, I'm just trying to boost my post count. HAHA!
     
  19. Touche !!!
     
    Bandit Billy likes this.
  20. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    If the ground is disconnected at the battery, as Ralphie pointed out above, then no other ground can "pop up".
     
    egads likes this.
  21. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    It's a battery disconnect switch, not a kill switch. You want a kill switch, install a kill switch.
     
    egads and Bandit Billy like this.
  22. XXL__
    Joined: Dec 28, 2009
    Posts: 2,117

    XXL__
    Member

    True (mostly*)... I guess I missed where we committed that the switch would be _at the battery_. Most that I've seen in real life were somewhere in the vehicle cabin or on a rear valance/bumper... some distance from the actual battery. In those cases, a ground cable that gets pinched because it is poorly routed, or perhaps cut when run through a panel because the installer doesn't know what a grommet is, and so on... then you get ground anyway.

    * carbon traces, easy arc paths like a battery post that is too close to the hood or fender, and so on.

    None of these scenarios can exist when you kill the hot side.
     
    egads and Blues4U like this.
  23. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    The same can happen on the hot side, and then you have instant problems that are a lot worse.
     
    egads likes this.
  24. 55styleliner
    Joined: May 11, 2015
    Posts: 563

    55styleliner
    Member

    Read any book about disconnecting a battery cable and it will always tell you to remove the negative cable first (on a negative ground system). The reason is so that you cannot accidentally short out your wrench on the car. Well, in my mind the same holds true for the disconnect switch. Put it on the negative side so that if the switch fails it doesn't start a fire. I haven't tried to kill a running engine with the switch on the negative side, I am going to test that theory later today. But if the battery is the only thing that completes the loop, any break, positive or negative should kill the engine.
     
    Bandit Billy likes this.
  25. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 12,287

    Bandit Billy
    ALLIANCE MEMBER

    These are good points and what I installed is a kill switch technically but of course it also disconnects the battery so it is both. In case the switch fails you must, MUST install a heavy circuit breaker between the switch and battery to protect the system and the car. Mine has a 120 amp breaker in the trunk that all power routes through after leaving the kill switch.

    Report back if that negative cable being removed kills the running motor. I did a lot of research on the install of these switches for a OT car I race from time to time. It's battery is in the trunk as well and NHRA requires a "kill switch" to pass tech in case I crash and burn. They don't care if the electrical system is off, they want the motor shut off and the electrical dead. My roadster is the 5th car I have wired this way (all trunk mounted batteries). Is it overkill for a street car, yeah maybe, but I feel secure knowing I installed one hell of an electrical system.
     
    55styleliner likes this.
  26. This is typical post from a dumb ass that is too lazy to READ THE RULES..either too lazy or too stupid...
     
  27. 55styleliner
    Joined: May 11, 2015
    Posts: 563

    55styleliner
    Member

    So I tried killing my engine when it was running by flipping my disconnect switch that is on the negative battery cable. Flipping the switch didn't even cause a misfire....... I may have to rethink this, or keep in mind that it is not a "kill" switch, but rather a "battery disconnect", which it does do for storage.
     
    Bandit Billy likes this.
  28. 05snopro440
    Joined: Mar 15, 2011
    Posts: 1,543

    05snopro440
    Member

    For anyone reading this, those posts at the start about the only way to retain memory being by switching the positive and running a fuse across it are wrong.

    You can easily do the same on the negative. The fuse and power don't know which cable they're installed on. Mine has been like that for 28,000 Km's and counting without any issue. And to add to the discussion, I prefer the negative. As many have said, it's not a kill switch. If you want to kill the motor, then that's a different purpose. I have a battery disconnect with a key for anti-theft purposes. When you remove a battery or are working on a car and need the battery unhooked, you always remove the negative post first. That removes all danger from the system. Same with a disconnect switch. Sure it works by switching the positive, but there's still danger in the system as the system is alive (as was said, electrons flow from negative to positive).
     
  29. Mike VV
    Joined: Sep 28, 2010
    Posts: 3,029

    Mike VV
    Member
    from SoCal

    I talked to a friend that has both worked in tech for NHRA national event races and owned his own electrical shop for 25+ years.

    While the NHRA says on the positive side, he has installed them both ways over the years and found no difference in the way...shutting down the power works.

    BUT... The way the switch and wiring is connected does make a difference.
    It would take a 5 page book to write out all of the different scenarios, to keep the various electrical items working, while actually shutting down the main power, which I'm not gonna do.
    It can be done basically the same way on either the pos. or neg. side.

    If you are running within the NHRA, run the switch on the positive side...period.
    If you just want a positive cutoff switch, either side of the electrical side works the same way.

    Just pay attention to the actual wiring to keep non-engine electronics working, but also shuts down the engine if turned off.

    Mike
     
  30. 392
    Joined: Feb 27, 2007
    Posts: 1,206

    392
    Member

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