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Technical Coil Wiring Help

Discussion in 'Traditional Hot Rods' started by fyrffytr1, Oct 27, 2019.

  1. fyrffytr1
    Joined: Dec 20, 2016
    Posts: 834

    fyrffytr1
    Member

    I am trying to get the straight 8 in my 39 Pontiac running and I need some help with the coil wiring. The previous owner hooked up the coil as shown in the picture with the wire from the - side going to the distributor and the +side is just hanging loose with a round eyelet terminal on it.
    The original coil is still on the firewall and has one connection that I guess went to the distributor. There is another connection on the side of the old coil that goes through the firewall and I am guessing it would have gone to a key on voltage source.
    My question is; is the new coil wired right with the - side going to the distributor and where could I hook up the positive side so I can see if this motor will come back to life? coil 1.jpg coil 2.jpg coil 3.jpg
     
  2. tubman
    Joined: May 16, 2007
    Posts: 6,914

    tubman
    ALLIANCE MEMBER

    I believe that 6 volt Pontiacs were negative ground. That being said, if there is a battery in the car, which post is connected to ground? that should tell you right away. Since closing the points grounds the primary ignition circuit, the coil should ground the same way as the battery. But you never know, a lot has happened to most of these cars in the last 70 years.
     
  3. 302GMC
    Joined: Dec 15, 2005
    Posts: 7,856

    302GMC
    Member
    from Idaho

    If it's neg. grd, - term. goes to dist.
     
  4. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    What ever side the ground cable at the battery is hooked to is the side of the coil goes to the distributor.
     

  5. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    ^THIS^ is an always with no exceptions. It also helps you tell what the ground on the battery is on a rig that didn't come with a battery but has all the ignition wires connected.
     
    Mark Yac and Black_Sheep like this.
  6. The + post/wire from coil goes to /from the switch. The - to the distributor. For testing purposes, I use a jumper from the + on the battery to the + on the coil. Eliminates all other wiring problems. Unhook to kill engine

    Ben
     
  7. Is it still 6volts? Don't be afraid of hooking up 12 volts to the starter to get it fired up. Use a 12 volt coil, and as long as you're not cranking for more than 10 seconds without a rest, it will be OK. It will crank and catch a lot quicker.
    Just make sure you don't feed the 12 volts to anything else (if it's still 6 volts), or you will start popping bulbs, etc.
     
  8. fyrffytr1
    Joined: Dec 20, 2016
    Posts: 834

    fyrffytr1
    Member

    There is no front end on the car.I really just want to see if the motor will fire up. If it does then it will be easier to sell f I decide to part with it.
     
  9. fyrffytr1
    Joined: Dec 20, 2016
    Posts: 834

    fyrffytr1
    Member

    OK. I have power all the way to the distributor but no fire through the points. I am headed to town for supper and will pick up a new set of points and condenser. The motor did run for about two seconds earlier today so that is a good sign.
     
  10. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 6,250

    Ebbsspeed
    ALLIANCE MEMBER

    Of course no one ever considers if the coil they are using is wired internally for a positive or negative ground machine. Note the image below, showing one side of both the primary and secondary windings connected to the + terminal on the coil. Note that while a coil will work connected in either polarity, there ARE coils that exist which are wired internally specifically for positive ground vehicles. Actually the internal wiring is the same, but the + and - terminals are labelled differently.

    You can test for correct polarity of the ignition coil by using a voltmeter. Connect the negative lead to the (-) negative terminal and the positive lead to the engine block.
    Set the meter on the highest volt range (these connections are the same whether you have a positive ground or negative ground electrical system). The secondary winding's polarity, which you are testing, is determined by the combined hookup of the battery and primary windings.
    Crank the engine over (do not start it) and the needle of the voltmeter should show an upward swing to the plus or positive side (do not worry about taking a reading). If volt the needle swings down to the negative side and gives a negative reading, your coil is hooked up backwards. To correct the polarity, simply reverse coil primary leads.
    A coil with reversed polarity will have about a twenty percent lower output which may not show up at idle and low rpms, but can cause an engine to miss or stumble under load and at higher engine rpms.

    There is also some "pencil lead" test that can be done, but I don't recall the "how to" of that process.

    Coil.jpg
     
    Last edited: Oct 28, 2019
    fyrffytr1 likes this.
  11. fyrffytr1
    Joined: Dec 20, 2016
    Posts: 834

    fyrffytr1
    Member

    Thanks for that information.
     
  12. brading
    Joined: Sep 9, 2019
    Posts: 704

    brading
    Member

  13. fyrffytr1
    Joined: Dec 20, 2016
    Posts: 834

    fyrffytr1
    Member

  14. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    The "pencil test" looks like a good way to get zapped.

    Analog voltmeter is the way to go. Connect the negative lead to the plug terminal itself and the positive to the block.

    IMG_1151.GIF
     

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