Un-hacking ignition wiring

Electrical and Ignition

  1. Swingin73Dart

    Swingin73Dart Well-Known Member

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    So I started to dive into trying to make my ignition wiring right today and found out just how strangely some previous owner butchered it. The car ran and appeared to charge when I first got it but the factory ignition module and ballast resistor were completely eliminated from the system. As was the harness and large plug (my factory manual calls it the “dash to engine connector”). The distributor appeared to be taking power from the ignition coil when the old 318 was still in the car too. And when I had hooked up the battery to wire my radio and a couple things inside the car I got no voltage when the key was in “on” or “accessory” unless I ran a jumper from the positive side of the battery to the battery wire for the alternator.

    I had taken almost every scrap of wiring harness off the parts car I had before it got scrapped but not everything appears to be there. I’m also pretty sure this is a factory 40 amp alternator car. That doesn’t bode well for me. I have an electric fuel pump and plan on running an electric fan. Those 2 things alone are over half of the charging capacity.

    So my questions are, where would the “dash to engine connector” go to after the ignition module side of the plug? And what would be the easiest way to upgrade the charging system to say, 100 amps? I’m seriously debating biting the bullet and just running a self contained distributor like a pertronix.

    Picture of the plug I mentioned.

    1AAB426B-3987-4233-AC58-9B9B6AD0FD89.jpeg


    The large wire I’m assuming is the battery wire to the altetnator and it’s cut off after the plug and looks to have been fried. 2 of the wires I think go to the positive and negative on the coil, one goes to the temp sender and it looks like the others may go to field on the alternator and the voltage regulator? It was like this when I pulled the harness from the parts car. And I’m tired of staring at wiring diagrams scratching my head so I’m turning to the experts. Any help is really appreciated. I’m sure we have all cursed bubba the electrician when we find stuff like this on our cars.
     
  2. moparmat2000

    moparmat2000 FABO Gold Member FABO Gold Member

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    You might be better off buying a new dash and engine compartment harness, repair the body harness.
     
  3. Swingin73Dart

    Swingin73Dart Well-Known Member

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    At this point the car is t really nice enough to dump the money into that. If I can work with what I got to make it functional and safe for cheap that’s what I’m gonna do.
     
  4. pishta

    pishta I know I'm right....

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    It was common to bypass that plug for the ammeter/volt meter hack, as well as changing to electronic ignition with an electronic regulator. Easiest way is to get yourself a roll of 18g stranded and start running replacement wires per the electrical schematic. Take your time and get a crimper and lug kit from HF or amazon. Solder everything you can, the bullet connectors only go so far. also get some multi color electrical tape so you can label the same colored 18g wire at the junctions so your schematic will make sense to you 5 years from now. Being a telephone man makes this the easiest method for me as I run, repair and trace wires all day out in the field.
     
  5. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    100A Run about a no6 wire WITH an appropriate fuse or breaker direct to the battery from the alternator. Read the MAD article on the whys and whats of bulkhead connector (firewall connector) failure, as well as the ammeter

    Catalog

    You are going to want to reduce voltage drop to the ignition system and just as important, the VR ignition terminal (unless you are swapping to a one wire alternator) Use the "ignition run" line to key a relay, and power the ignition/ alternator field/ VR off that relay, fed with a fuse/ breaker off the starter relay "big stud."

    I DO NOT particularly like "one wire" setups. The "sense" is the only wire, so this wire MUST be "big" in that case to reduce voltage drop and keep the sensing within bounds.

    WHERE IS that connector you pictured? Is this under the hood? If that is "that" one, then eliminate it. Just splice / replace damage the wires and cut out the connector. In this case leave it out. It was a REAL bad idea

    And, are you still trying to wire up the ignition / resistor? We can get you some diagrams, go over to MyMopar and download free service manuals if you don't have, as well as aftermarket wiring diagrams and some simplified ones concerning the ignition.

    At this site, bare minimum, you want to look at service manuals and electrical

    MyMopar - Mopar Forums & Information - MyMopar Tools/Reference

    And browzing through those tech bulletins (Master tech) is not a bad idea
     
  6. Swingin73Dart

    Swingin73Dart Well-Known Member

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    I really couldn’t say where that connector is supposed to be, that part of my harness is off my parts car as it still had the factory ignition intact. And I just stripped everything off the car and sent it packing. I think my 73 factory manual has a simplified ignition schematic I can use.

    F2FCF15C-5180-47B7-A206-25D9146318C8.jpeg

    If this is right I should be able to run all these wires direct from the module and eliminate that plug entirely using the factory harness
     
  7. Swingin73Dart

    Swingin73Dart Well-Known Member

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    Rewiring this to be right isn’t my issue, I’m just a terrible diagnostician when it comes to things not being where they should and shoddy PO wiring jobs. I’m reasonably competent and always wire things in nice and neat with clear seal connectors and heat shrink tubing. I know solder is the “best” way but I’ve never had any problems with things I’ve wired years ago that see regular use.
     
  8. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    The schematic, like most of the schematics calls the main circuit 'Battery'. The Power supply is actually Battery or Alternator.
    On a '73 a-body those feeds join at a welded splice. The alternator wire is 12 or 10 gage.
    upload_2020-2-17_9-59-10.png

    Since you will be running additional electric loads, you probably want a different scheme. The standard '73 scheme routes the power feeds inside the car, and then out again through the bulkhead connector tothe engine compartment. Not a big deal if just running ignition and field, with occassional battery charging. Thats a long route with lots of connectors for 40 amps all the time. You probably want a setup with relays and a fuses in a auxillery box under the hood. The B-body fleet type wiring is worth looking at. Even with the high-output alternator type wiring scheme, you probably don't want to use a factory ammeter because the equipment will be sucking 40 amps from the battery and then recharging repeatedly.
     
  9. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    That's right. There are fewer and fewer 'actual' 5 pin modules which require a 4 pin resistor. Most any module you run into anymore, unless it's an old one, are 4 pin, which can use a 2 pin resistor. If you can mock it up to run, and leave the resistor feeding back to the module disconnected, you'll know for sure. Otherwise you can check resistance between the resistor feed to the module and the other pins. If they are all open, it's a 4 pin module. The module MUST be grounded to run.

    Also, the half dual resistor going to the coil is really the same as the old points system. That is, ign1 feeds the resistor and that feeds the coil. The IGN2 hooks to the resistor on the coil side, and that is "hot" during cranking. This feeds "hot" battery voltage to the coil directly during start, and BACK feeds power through the resistor and back around to the module for starting.

    What I mentioned earlier, "IGN 1" shown in your simple diagram, is another problem. The path for that originally was the big red battery feed---through the bulkhead---to the under dash welded splice---to the ignition switch---back out the bulkhead on ign1---each terminal point is a voltage drop potential. That point also feeds the alternator field and VR ign. If that point suffers voltage drop, it will cause an OVER charge condition. That is the circuit you should consider adding a relay.
     
    Last edited: Feb 17, 2020
  10. 66 Valiant wagon

    66 Valiant wagon Well-Known Member

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    I used an MSD 6A box and a one wire 100 amp alt in my 72 B body. It was super easy and eliminated most of the factory engine harness. I just have that stuff taped up and out of the way. I'm using the stock points distributor. Maybe that's the lazy way out but it worked for me. It is a pricey initial cost but it can be pulled and swapped to any other car if I decide to go another route in the future.
     
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