Ignition Module for Antique Car

Discussion in 'The Projects Forum' started by modelafords, Jul 31, 2009.

  1. modelafords

    Thread Starter New Member

    Jul 31, 2009

    I'm a newbie to the forum and electronic circuits but I'm trying and willing to learn. I have a 1931 Model A Ford coupe that I'm trying to figure out how I can convert its distributor over to electronic to make the car more road worthy and have parts available at most autopart stores in the event of being broke down on the side of the road. The distributor is a rather rare Mallory dual point distributor and finding points for it is near impossible.

    From my searches on Google I've come across some info on using a Chrysler pickup coil and reluctor inside the distributor and using a GM HEI module to trigger it. All of this sounds good but it requires a negative ground system, where I have a positive ground system.

    I have talked to some people and found out that the HEI module will work on a 6 volt system, but not a positive ground system. I'm told inside the HEI module there is a signal converter and that it is polarity sensitive. I'm attaching a picture of the HEI module and I would like to know how I could go about changing this design or building my own module to allow it to work with a postive ground system.

    Any help or info would be appreciated. Thanks.

  2. jpanhalt


    Jan 18, 2008
    What devices in the car require a positive ground? The simplest thing would be just to change the ground. John
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    I'd agree, if you are not keeping it 100% original then going to negative ground makes things easier.

    It should be dead simple as long as it has a conventional dynamo.

    If that has one larger output terminal and one smaller field terminal, then all you should have to do is disconnect the dynamo terminals, reverse the battery connections, then temporarily connect a wire from the battery positive to the dynamo field terminal.

    Try ten or fifteen seconds, then give it a minute to cool and repeat three or four times. After that, reconnect the original wires and try it out.

    The idea is to reverse the residual field in the dynamo so when the engine starts you get a positive output to charge the battery, rather than a negative output and things smoking unpleasantly..

    If the dynamo has anything other than two terminals and ground, I'd check with a specialist to find which connections are the field winding (unless it's obvious).
  4. jj_alukkas

    Distinguished Member

    Jan 8, 2009
    Simply reversing terminals would need isolation of devices from chasis. Most equipments on not-so-modern vehicles have a metal case which is internally grounded.
  5. Externet

    AAC Fanatic!

    Nov 29, 2005
    The modern 12V GM HEI module on your link may not be the convenient one for your polarity and voltage.
    Do a search for the points-to-electronic ignition conversion kits, some brands are:
    They should be capable of making your car happy.
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    jj_alukkas: Yes, grounded metal cases BUT a loong time before semiconductors - nothing is polarised.

    Bulb filaments don't matter, electric motors in cars almost universally have wound fields so run the same direction regardless of polarity.

    I have done this many times on cars from the 50s and 60s (to fit negative earth radios) and never encountered a problem.
  7. modelafords

    Thread Starter New Member

    Jul 31, 2009
    Thanks for the info. I thought about changing over to a negative ground but was wondering if there was a way to do it with a postive ground if I was to build a simple module with a npn or pnp transistor. The reason why I'd like to go with the Chrysler pickup coil and reluctor with a GM HEI module and not a Pertronix, Mallory and so on is because if I was to break down out in the middle of nowhere I would be able to get parts at just about any autoparts store for it. If I built a module I'd just carry a spare with me.

    I'm attaching a picture of the wiring of the car. If I was to go with a negative ground wouldn't my ammeter read backwards or would I just change the wires there to?

  8. SgtWookie


    Jul 17, 2007
    Yes, you would need to swap the wires around on your ammeter.

    It shouldn't take 15 seconds to flash the generator field, either - just a few quick blips should be more than enough.
  9. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    Hi, yep I forgot about the ammeter...

    You would have to lift the brush in the 'third brush' position of the dynamo and connect battery positive to the brush holder to repolarise it.

    Re. the time, I have seen on rare occasions where a quick flash does not work but several long ones do.. It could be heat build up having some effect.
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Aren't you overcomplicating it? Just use a points distributor (from any '60's or '70s car) instead of the electronic distributor.

    Then nothing else is polarised, you can use points -> ignition coil and just run it in your positive ground car.