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Ignition Coil Wiring Question (w/ Diagrams)


Earl Gray

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UPDATE: 4/11/20

Final analysis and solution below.

_____

Original post:

 

I have a '51 Dodge Coronet (D-42) with gyromatic that's been converted by the previous owner to 12v with one-wire alternator. If you have a link to a previous post about the issue/questions below, please share.

 

Issue: No spark from 12v ignition coil (with required external resistor in place and properly installed).

 

What happened?

When I got this car, there were some wiring issues. My car stalled/died at a stop due to the transmission downshift. According to the late and very knowledgeable Don Coatney's pictures, he wired his ignition coil (-) to distributor and (+) to external resistor/power. Here's the link to his pictures: https://smg.photobucket.com/user/DonCoatney/media/Engine/dimple.jpg.html?sort=3&o=80

 

When I bought the car:

  1. The black wire from the circuit breaker/resistor unit was connected to the ignition coil's (-) post.
  2. The green wire from the circuit breaker/resistor unit was not connected to the ignition coil but just hanging out, not attached to anything.

 

Just today, I connected the 

  1. Black wire to the (+) ignition coil post
  2. Green to the (-) ignition coil post

 

And it did what it was designed to do...didn't stall/die at a stop and shifted way better then before.

 

Then...a few blocks from home...it died. No spark at the ignition coil center.

 

The Dodge service manual has four different wiring diagrams:

  1. For the D-29
  2. For the D-30
  3. For the D-33 & D-34 (photo 1)
  4. For the D-41 & D-42 (photo 2)

 

The first three wiring diagrams in the service manual have the same details regarding the ignition coil(+) to the distributor and (-) to firewall (horn relay?). However, the wiring diagram for the D-42 doesn't show the ignition coil's polarity for some reason (see photo 2).

 

Also, regarding the circuit breaker/resistor unit, the black wire is shown in the diagram to connect to the (+) post and green to the (-) post. That's why I did it this way.

 

Again, when the black and green wires were connected as mentioned above, the anti-stall worked perfectly and it shifted way better. Amazingly so! I need to buy a new ignition coil. I'd like one that doesn't require an external resistor like the NAPA Part# MPE IC14SB (Thankful for grey beard's suggestion from January 1, 2010)

 

Questions:

  1. Is it required to switch the ignition coil wiring to (+) wire to (-) post and (-) wire to (+) post when converted to 12v?
  2. Do the black and green wires switch too? If so, how does this affect anti-stall, kick-down, and other components for the carb and gyromatic?
  3. What horn relay replaces the OEM?

 

20200407_173036.jpg.37f9ab70145cd07b4ceb47b9880348a7.jpg20200407_173017.jpg.29b54e5040e0ccc5c3caeff8a5c1ce22.jpg

Edited by Earl Gray
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1. No, it is only required when you change the polarity of the ground.  You car went from 6v positive ground to 12v negative ground, so the points need to be hooked to the coil - terminal.

 

2. I know nothing about the trans setup, sorry.  But it may be wise to thin k about the change in both voltage and polarity's effect on that system.  Others more knowledgeable will hopefully chime in.

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I've had a resistor break and stall a cold car. They can weaken with age or from abuse. It did not restart.

When the resistor warmed up, the car would start. The resistor wire was just making contact when it felt the right temperature.

 

I have had coils fail that way too. Car doesn't want to run, then just quits. Internal coil break.

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Do you regain spark if you unhook the black and green wires?

If so you'll know the issue is in the tranny circuit. Stuck kick down switch, shorted solenoid....etc. likely something causing the coil to remain grounded. 

Edited by 50mech
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Your Gyro-Matic has an interrupter switch, which momentarily grounds the distributor when the transmission is shifting gears.  Maybe the interrupter switch is always closed, or the circuit is otherwise.grounded.  It would help to look the transmission shifting diagrams in the shop manual, to see the function of the interrupter switch and its related wiring.   

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51 minutes ago, 50mech said:

Do you regain spark if you unhook the black and green wires?

If so you'll know the issue is in the tranny circuit. Stuck kick down switch, shorted solenoid....etc. likely something causing the coil to remain grounded. 

No. I rewired it back to what it was before the issue and no spark.

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37 minutes ago, DonaldSmith said:

Your Gyro-Matic has an interrupter switch, which momentarily grounds the distributor when the transmission is shifting gears.  Maybe the interrupter switch is always closed, or the circuit is otherwise.grounded.  It would help to look the transmission shifting diagrams in the shop manual, to see the function of the interrupter switch and its related wiring.   

Maybe. but what about the black and green wires? Do the black and green wires switch posts too? If so, how does this affect anti-stall, kick-down, and other components for the carb and gyromatic?

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1 hour ago, DonaldSmith said:

Your Gyro-Matic has an interrupter switch, which momentarily grounds the distributor when the transmission is shifting gears.  Maybe the interrupter switch is always closed, or the circuit is otherwise.grounded.  It would help to look the transmission shifting diagrams in the shop manual, to see the function of the interrupter switch and its related wiring.   

 

  Wasn't getting fire from the coil on my 41 Chrysler with vacamatic transmission, I removed the wire from the distributor that goes to the "ignition interrupting switch". That made the coil secondary circuit hot.

 

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7 hours ago, Earl Gray said:

No. I rewired it back to what it was before the issue and no spark.

If you get no spark with both of those wires unhooked and then the issue is with the coil or distributor (points). 

Wired back how it was , a stuck or faulty trans control component could still ground the coil.

Edited by 50mech
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On 4/9/2020 at 3:15 PM, 50mech said:

If you get no spark with both of those wires unhooked and then the issue is with the coil or distributor (points). 

Wired back how it was , a stuck or faulty trans control component could still ground the coil.

You're on to something. I disconnected the black and green wires that go to the circuit breaker/resistor unit and it started.

 

It's running right now. I'm parked outside my house and typing this as it runs.

 

Now what?

I'm going to run a resistor from the coil to the carb.

 

I'm still not sure which wire going to which post.

 

Before the issue...Black was connected to the negative post and the green was hanging free, no connected. I connected them according to the service manual and had the issue. I disconnected them both and the car started.

 

Since it's been converted to 12v, it's no longer a positive ground, so the negative post now connects to the distributor.

 

That being said, does the black and green wires switch now too, i.e., black now needs to be connected to the negative post and green to the positive?

Edited by Earl Gray
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UPDATE: I switched the wires coming from the carb to the coils to black on negative coil post and green on positive coil post.

 

Engine starts and column shifter switches between gears but the transmission acts like the hand brake is still on. Yes, the actual hand brake is disengaged.

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Now youll probably have to break out a meter. Check the black wires continuity to ground. I don't have any experience with these tranny's so just looking at the wiring diagram I'm guessing perhaps the interruptor switch is stuck as was suggested by @DonaldSmith.  Have to check it's continuity after disconnecting it. 

 

I don't think any of that circuit is polarity sensitive so it wouldn't have to be switched around on the posts....but I could easily be wrong there.

Edited by 50mech
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Update:

After hours of different tests and configurations, here's what I have.

 

I switched the black and green wires coming from the ignition coil and added a resistor. Black is on the negative coil post and green is on positive coil post.

 

Works great, shifts well, doesn't stall, and the kickdown works great too.

 

I was hoping to find someone with a D-42 with a 12v system and gyromatic to see how they have theirs running in the proper configuration. Hope this helps the next person. If there's any issue with this current configuration, I'll give an update.

20200411_151339.jpg

Edited by Earl Gray
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Final analysis and solution:

 

For a converted 12v D-42 with a Gyromatic, the black wire needs to be connected to the negative ignition coil post and the green needs to be connected to the positive ignition coil post. 

 

The black wire goes to the Interrupter Switch. The green wire goes to the governor.

 

When I wired according to the service manual (black to positive and green to negative) it killed the coil.

 

When I rewired it (switching black/green as stated above), everything worked.

 

When black and green were wired wrong, it grounded out the blue interrupter switch, which when done as a resistor test, kills the engine (see photos and alligator black test wire alligator clipped blue terminal to block ground).

 

Additionally, wiring it wrong made the transmission act like the handbrake was engaged when it wasn't. When this happened, I returned the wiring to base line (only black on negative post and green was hanging free) to get the transmission "unstuck." The "stuck" acting transmission probably happened by the overload to the governor, since the grounded blue only kills the engine/ prevents it from starting.

 

I'm not an expeat but I've learned along the way and it's running well. If you have experience with this, please drop a comment.

20200411_172514.jpg

20200411_172522.jpg

Edited by Earl Gray
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Great to see it fixed and operating as it should.  It does reinforce that these transmissions are mechanically sound and reinforces the common wisdom that most of their faults are external and though frustrating are relatively simple and inexpensive to repair.  Pretty impressive for 70 year old technology.  Thanks for the updates and follow up.  Maybe one of the kids can copy your thread to the tech archives.  Appreciate your perseverance.  Enjoy your ride.

 

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@greg g,

Though it was frustrating at times, looking back, it makes sense how it wasn't working.

 

You're absolutely right. These transmissions work well and are simple. The transmission issues were operator error.

 

I'm just not too sure if the ballast resistor on the black wire is doing much. My multi-meter didn't read any change. My thinking was to add the ballast resistor to protect the transmission components from 12v when they were meant for 6v. Overthinking or underthinking? I'm going to test:

1. Both black and green with their own ballast resistors.

2. Both without the ballast resistors

 

...and provide an update.

 

I'm sure someone else out that's more knowledgeable and experienced then me can jump in about the placement and effectiveness of how it's currently wired.

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Speaking just from an electronic standpoint here.

Resistor is a good idea but needs to be matched to do much good.

You'd need to activate the solenoid, measure the current then

Actual measured voltage divided by measured current gives you the solenoids effective resistance (impedance really but that's another story) 

You'll need a resistor with about that same value that is able to handle the power (watts).

Voltage x half the current you measured plus some safety margin will give you the required watt rating.

 

Some guesses;

1. since the interruptor switch is originally fed through a 12ohm resistor you're going to need something in the neighborhood of another 12-24 ohms.

2. The one you're using is less than 1.5ohms 

3. You're gonna need maybe 15 watt

 

If im in the right neighborhood LED headlight resistors in series might make a good option...autozones and such have them on the shelf, they're usually 6ohm each and 15watt and around $15 a pair.

 

 

 

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