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Technical Pos ground to neg ground

Discussion in 'The Hokey Ass Message Board' started by Boden, Oct 3, 2019.

  1. Boden
    Joined: Oct 10, 2018
    Posts: 747

    Boden

    How do I switch from positive ground to negative ground?


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  2. theboss20
    Joined: Dec 30, 2018
    Posts: 274

    theboss20





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  3. theboss20
    Joined: Dec 30, 2018
    Posts: 274

    theboss20

    What car?


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  4. treb11
    Joined: Jan 21, 2006
    Posts: 3,948

    treb11
    ALLIANCE MEMBER


  5. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,535

    Doublepumper
    Member
    from WA-OR, USA

    ^ You win the internet today!:D
     
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  6. Boden
    Joined: Oct 10, 2018
    Posts: 747

    Boden

    1953 ford Customline Tudor. Souped uo flathead


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  7. From what I understand, obviously switch your cables, then switch the wires on your ignition coil and ammeter. I’m not certain on the fuel gauge or radio because the only times I’ve done this is on old Farmall tractors. Are you going 12 volt as well?


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  8. KJSR
    Joined: Mar 7, 2008
    Posts: 2,494

    KJSR
    Member
    from Utah
    1. Utah HAMBers

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  9. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    Since it's a Ford, it should not care about polarity on the gauges, since they're thermal, not magnetic.

    The original AM radio will give you the most trouble. Or, it would, if it worked.

    (I think they got it all covered--reverse wires on the coil, and the ammeter if it has one, and everything else will be fine)
     
  10. Boden
    Joined: Oct 10, 2018
    Posts: 747

    Boden

    Ok. And yes it is 12v. What about the generator wires?



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  11. theboss20
    Joined: Dec 30, 2018
    Posts: 274

    theboss20

    The generator wires are fine...but you may have to re-polarize the generator because of the change...


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  12. Flathead Dave
    Joined: Mar 21, 2014
    Posts: 3,959

    Flathead Dave
    ALLIANCE MEMBER
    from So. Cal.

    Attached Files:

  13. plym49
    Joined: Aug 9, 2008
    Posts: 2,802

    plym49
    Member
    from Earth

    DO NOT switch the wires on the ignition coil. The coil is an autotransformer and switching the leads produces lower voltage to the plugs. The coil, as an electromagnet, does not care about the polarity. As an autotransformer, it does care about which lead goes to ground.
     
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  14. Be careful or your car will run backwards
     
    Last edited: Oct 3, 2019
  15. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    :confused::D:rolleyes:o_O:)
     
  16. WB69
    Joined: Dec 7, 2008
    Posts: 1,958

    WB69
    Member
    from Kansas

    Reversed my avatar and works great. Did have to change the generator polarity.
     
  17. Your horn will go !KNOH
     
  18. Hotrodmyk
    Joined: Jan 7, 2011
    Posts: 2,302

    Hotrodmyk
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    1. Northwest HAMBers

    Horn may suck instead of blow :eek::D
     
  19. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    Then why does it say + and - on the coil not s and d for switch and distributor I have always been told a coil is not as efficient hooked backwards. On an AC transformer power goes through the primary side both ways. To change direction of a dc motor you reverse polarity your heater may be interesting.
     
    Last edited: Oct 3, 2019
  20. tubman
    Joined: May 16, 2007
    Posts: 6,916

    tubman
    ALLIANCE MEMBER

    The only reason to go from positive ground to negative ground is if you are switching to 12 volts. If you are not going to do that LEAVE IT ALONE. I know you are a young guy getting into our hobby, and that's to be commended. However, it seems that you are reacting to just about every off the wall post on here you have seen. If I were in your position, I would leave everything as close to stock as I could to reduce any complications in what you are trying to do.

    The first thing you should realize is that no matter what you do, you are not going to end up with anything close to a "tire-fryer" with any flathead in a '53 Ford. Not enough power and too much weight. Just try to end up with a good looking, nice running vehicle. Trust me. you'll be miles ahead setting your sights a lot lower.

    Bottom line? If you are really after performance, scrap the flathead and build a 350 Chevy.

    I do NOT recommend this route, but it is the cheapest way to get a performance vehicle.
     
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  21. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway


    An ignition coil doesn't have a polarity as such, that is it will work connected either way. It does matter in terms of spark energy at the plug. Electrons like to jump from hot to cold, so an ignition coil hooked up "wrong" might be down by about 15 - 30% under load but strangely enough - this doesn't have anything to do with whether the car is negative or positive ground! I don't understand it either really. Has to do with the common connection inside the coil. There's a couple ways to check. The "pencil" method looks like a dependable way to shock the shit out of someone if not careful. Analog voltmeter works fine.

    https://mgaguru.com/mgtech/ignition/ig104.htm

    The MGA With An Attitude
    MGAguru.com MGAguru.com
    IGNITION COIL POLARITY - IG-104

    There is some misconception about ignition coil polarity and how important it may be (or not). For most people it is only a matter of lack of knowledge, perhaps followed by getting some bad information. How the coil works (with points and condenser) to create a high voltage spark is covered in another article. This article is a discussion about electrical polarity of the coil and spark plugs.

    [​IMG][​IMG]
    The ignition coil is essentially a low voltage to high voltage transformer with about 100 to 1 ratio of windings and voltage. The coil case is not grounded, and both primary and secondary windings inside are "floating" or isolated from the case. The only thing the windings have in common is one end connected to the same primary terminal, and it really doesn't matter much which one. Being a transformer it must have pulsating or alternating current to work. Initial pulsating is done by connecting and disconnecting the primary circuit ground connection. Alternating current then comes into the function in a big way by electrical "ringing" in the condenser at very high frequency. A transformer is not affected by polarity, since it is an alternating current device, so it matters not to the transformer what the input or output polarity may be. Any polarity on the primary side and any polarity on high tension side will produce the same quality of spark.

    Why then do we worry about coil polarity? Because the spark plugs do care which way the electrons are flowing in the high tension circuit. The spark plug has a thermally insulated center electrode (surrounded by ceramic). With engine running the center electrode runs substantially hotter than the exposed end electrode. Design of the ceramic insulator determines how hot the center electrode will run, leading to the designation of hotter or colder spark plugs. As electrons go, they love to jump away from a hot surface and fly toward a colder surface, so it is easier to drive them from hot to cold rather than from cold to hot. End result is a difference of 15 to 30 percent in voltage required to make spark "initially" jump the gap on the plug depending on which way it is going. So the spark plug prefers to see a voltage potential that is negative on the center electrode and positive on the end electrode for the very first hop of the spark. Oddly enough, this has nothing to do with polarity of the vehicle electrical system, but it is influenced by the common connection inside the ignition coil.

    The common knowledge bit about electrons is that they carry a negative charge. For electrical bits (similar to magnetic bits) opposites attract each other and negatives repel. This means the direction of flow of electrons in a car is from the battery negative post through the wiring to the battery positive post (not necessarily intuitive). If you reverse cable connections on the battery the current flows in the opposite direction through the vehicle wiring. For most original functions on the MGA this matters not one whit to anything, as most original equipment in the MGA is not polarity sensitive (except maybe the optional radio). As one end of the primary winding in the ignition coil is connected to one end of the secondary winding, reversing polarity of the coil primary side will reverse the drive direction of the spark current on the output side (even though current in the vehicle low voltage wiring still flows the same way).

    So reversing vehicle electrical system polarity will reverse direction of spark drive. The engine still runs either way, but spark might be more reliable under marginal conditions if you get it right. The simple fix for this is to reverse the two primary wire connections on the ignition coil. Because the output spark is very much higher voltage (20,000v) than the car battery (12v), it doesn't care if the battery polarity is helping or hindering by a meager 12 to 14 volts in battery potential.

    So how do we know which way to connect the ignition coil for best results? Original production coils were generally marked on the primary terminals "SW" for Switch and "CB" for Contact Breaker. This was assuming the vehicle wiring was connected for positive earth (positive battery cable grounded on the chassis). If you reverse battery polarity (going to negative earth), then these coils need to be connected with "CB" to the ignition switch and "SW" to the distributor points wire. Later issue ignition coils are marked "+" and "-" on the primary terminals. These are more no-brainers, as you only need to match the terminal markings to the battery posts. For positive ground the "+" terminal goes to the distributor (to be grounded on the engine block). For negative ground the "-" terminal goes to the distributor (to be grounded on the engine block).

    [​IMG][​IMG]
    If you are still skeptical about all this, there is a quick way to check directly which way the current is flowing in the high tension circuit. Disconnect a spark wire from a spark plug (or the coil wire from the distributor cap). Hold this HT wire near a grounding point (or near the connector end of a spark plug), and position the tip of a graphite pencil in between. When you crank the engine (no need to start or run) you can observe the resulting spark jump between wire and pencil, and between pencil and ground (or spark plug). A flare (hard to see) toward the plug (or ground) shows correct polarity while a flare toward the coil shows reversed polarity. If the flare goes toward the coil, just switch the primary wires on the coil and make note of the connections for future reference.

    [​IMG][​IMG]
    Can't see the flare? Not sure yet? You can also check spark polarity using an analog (moving needle) volt meter. Hook up a voltmeter with the negative lead to the plug terminal and the positive lead to the block. Set the meter on the highest volt range. Crank the engine over (no need to start it), and you should see an upward swing of the voltmeter needle (don't be concerned with taking a reading). If the needle swings down off the scale, your coil is hooked up wrong. To correct it reverse coil primary leads. Do not worry about the coil markings, but make note of them for future reference.

    ______________


    SO, while it is important to connect an ignition coil correctly for optimum spark, nothing gets swapped around when converting to negative/positive ground.

    Field wound electric motors - engine starters and heater blowers - don't care about polarity, they will work fine.
     
  22. tubman
    Joined: May 16, 2007
    Posts: 6,916

    tubman
    ALLIANCE MEMBER

    WOW! I'm impressed! Too bad that it probably doesn't help the O/P one bit.
     
  23. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Yeah, I cut n' pasted just a small paragraph from that article and for some reason the whole page went through, I just said what the hell and left it.
     
  24. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    Are all automotive coils not grounded through the case? The reason I ask is the Y block in my 56 Bird got to acting up and at night I saw sparking at the coil mount at the intake. I tightened the bolt holding the coil and the car ran fine.
     
  25. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    No, ignition coils aren't grounded. There is only one common connection between the two coil windings.

    Ignition or high voltage is strange stuff. If it's arcing to ground, or cross firing, it can be quite a few things. The fault will either come back, or appear somewhere else most likely. If you can find someone with an ignition scope it can find all sorts of defects pretty quickly.
     
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  26. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    The car is long gone but the problem never resurfaced until about 2 years later I replaced the 292 with a street hemi.
     
  27. COCONUTS
    Joined: May 5, 2015
    Posts: 1,163

    COCONUTS

    This is one item that always confuse me, ever since I took Auto Shop, is which way to hook up a coil. Every repair manual and auto text book, I have ever look at, will show a ignition system wiring diagram without the + and - on the coil much like Truck64 did in his first diagram. So now I am guessing that it all depends on if the engine has a positive grounded system or a negative grounded system. So in my case, everything I own has a negative ground setup and the wire from the negative terminal on the coil is the one that goes to the distributer (to be grounded on the engine block). I think I would go with the volt meter test to determine spark polarity. Excellent job Truck64
     
  28. theboss20
    Joined: Dec 30, 2018
    Posts: 274

    theboss20

    No matter if the power comes from Ground side or otherwise the source is still the Pos. post of the battery....so I always look at it as Power to the + terminal and the - terminal to the distributor.


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  29. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    Great informative post, thank you!
     
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  30. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    I think it might have been Jim @GMC BUBBA, who mentioned something about this, too - as I recall, something to do with the primary wire is wound around an iron core so connecting it "wrong" can result in a semi-permanent reduction (magnetism?) in output or somesuch, despite re-connecting properly. Could be mis-remembering. Does any of this matter? Heck if I know.
     

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