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1969 Mustang Convertible 302 T5
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Discussion Starter #1
I could use some help here. I have a Pertronix igniter III (cast look) and was using a stock coil for awhile without any issue. The resistor wire was bypassed at the ignition switch (spliced separate wire) when I converted to the Pertronix.

I switched to a Flamethrower coil thinking it was simple upgrade to a very old coil and would match well with the Igniter III. When I started the car for the first time, it ran for about a minute and then stopped. When I attempted to restart it, it fired off but never started. I immediately suspected the coil because it was the only thing that has changed. I checked the ignition wire voltage at the coil with the key on and it read about 7 volts. I jumpered the pos+ coil terminal to the battery and the car started/ran perfectly.

  • I removed the pos + ignition wire and check it again with voltmeter (key on) and it reads 12v.
  • I try starting the car - doesn't start. Checked ignition wire voltage again before shutting key off and it is about 7v.
  • I remove the ignition wire from the coil and test it - and it reads 12v.
  • I hold the ignition wire and positive distributor wire together, off the coil, and it measures 7v.
  • Note: Aftermarket tach (neg) wire was removed early on during the troubleshooting to rule that out
Obviously something in distributor (circuit) is pulling the voltage down to a "no run" situation but only when using the ignition wire - because, as I pointed out above, when I jumpered the coil to the battery, it ran fine. By jumpering the coil successfully, is this still pointing to the ignition wire - event though I can read 12v at different times? Maybe a crap connection/splice at the resistance wire - that only presents itself when there is a large draw on it - but it didn't do it for the original coil? Do these coils put more demand on the feed side of the circuit?

Can someone help me by explaining what is possibly happening and why?
 

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Voltage in a closed circuit reflects the total resistance in the circuit. If your "Ignitor" is in "dwell mode" (circuit is complete and windings in the ignition coil are being charged) the voltage will reflect that one side of the circuit is, effectively, shorted to ground. If you have voltage at the ignition coil+ while cranking but no spark output I'd suspect the "Ignitor" has fried.
 

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When you have two items connected in series, which ever one has the highest resistance, drops the most voltage. The voltage drop be each device adds up to the source voltage. So when you read across the coil, you read the voltage drop of the coil. When you disconnected the coil and read 12 volts you basically replaced the coil for the meter. The meter has a extremely high resistance. So much so, anything else in the circuit might as well be a piece of wire, it doesn't matter. You're actually reading the voltage drop of the meter. So when you read a lower voltage, you're reading the actual voltage that device uses and that there is something else using voltage. When you read across the coil, the meter is not in series. It comes down to how you have the meter connected to the circuit. If in series, you will always read the source voltage. When in parallel you read the voltage on the device, not the battery voltage.

Since your car ran when you connected the coil to the battery says that the coil and Petronix are OK. The problem is with either the ignition switch or wiring from the switch to coil.
 

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1969 Mustang Convertible 302 T5
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Discussion Starter #5
When you have two items connected in series, which ever one has the highest resistance, drops the most voltage. The voltage drop be each device adds up to the source voltage. So when you read across the coil, you read the voltage drop of the coil. When you disconnected the coil and read 12 volts you basically replaced the coil for the meter. The meter has a extremely high resistance. So much so, anything else in the circuit might as well be a piece of wire, it doesn't matter. You're actually reading the voltage drop of the meter. So when you read a lower voltage, you're reading the actual voltage that device uses and that there is something else using voltage. When you read across the coil, the meter is not in series. It comes down to how you have the meter connected to the circuit. If in series, you will always read the source voltage. When in parallel you read the voltage on the device, not the battery voltage.

Since your car ran when you connected the coil to the battery says that the coil and Petronix are OK. The problem is with either the ignition switch or wiring from the switch to coil.
I will need to print this and keep it near my meter..... The car did run fine when I connected the coil to the battery. The resistor wire is bypassed under the dash, but I'm not exactly at what point. The ignition wire has a full 12v at the coil (when not attached with lead from distributor). The only thing that I changed was swapping the stock coil for the Flamethrower III coil. Like a dummy, I gave the stock coil away a few days ago - but I may be able to get my hands on it or another tomorrow to see if that is indeed the "x factor". Maybe the lower resistance with flamethrower III is not working with my wiring.

I also just learned about the pertronix relay. That would certainly eliminate the suspicion with the wiring. Does anyone have any negative thoughts on the relay solution? Where do you mount/hide one of these? I can't find any video or pics of it installed.
 

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1969 Mustang Convertible 302 T5
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Discussion Starter #8
What does this mean? The starter just turns the engine over, or the engine tries to run then dies when the key is released?
Sorry for the poor terminology: It "tried" to run but just died when the key was release. It only did this a few attempts and then stopped doing that. Right after that I jumped straight from battery to coil and it fired right up.
 

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Sounds like your bypass is faulty. You might try running the jumper from the battery (+) to the coil (+) again and start the engine, if it starts remove the jumper and see if it keeps running.
 

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Discussion Starter #10
Sounds like your bypass is faulty. You might try running the jumper from the battery (+) to the coil (+) again and start the engine, if it starts remove the jumper and see if it keeps running.
That's a good idea... I should have thought of that.
 

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Discussion Starter #11
At my ignition switch, if I needed to re-route the bypass wire, can I splice into the green/red stripe wire that shares the terminal with the pink ballast wire? It's a smaller gauge wire and I'm wondering if there is a risk involved with current draw.

(I still haven't tested the bypass by leaving key on when coil getting power from battery - that will happen later today)
 

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At my ignition switch, if I needed to re-route the bypass wire, can I splice into the green/red stripe wire that shares the terminal with the pink ballast wire? It's a smaller gauge wire and I'm wondering if there is a risk involved with current draw.

(I still haven't tested the bypass by leaving key on when coil getting power from battery - that will happen later today)

I added a y adapter. Two wires into one. One goes to the pink and one goes to the pertronix. My tach still works perfectly.
 

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Discussion Starter #13
I added a y adapter. Two wires into one. One goes to the pink and one goes to the pertronix. My tach still works perfectly.
I'm not sure what you mean. Are you splicing into the pink wire?
 

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Discussion Starter #14
I'm hoping someone could comment on the green wire with red stripe that shares the terminal with resistor wire (pink). Here is a picture of the back of my ignition switch. It would be easy enough to move my bypass wire over to this green/red wire. I'd rather splice then mess with the terminals.

755845
 

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Discussion Starter #16
Thanks much for that pic! My setup looks a little different. The green/red stripe wire is in the same terminal as the pink resistor wire. Would that indicate that we are talking about a different green/red wire? My concern attaching a 12 gauge bypass wire (recommended by Pertronix) to what looks like a 18-20 gauge wire. Should I worry about the current to be passed through the 20 gauge section? This might be unique for the 1969.
 

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Discussion Starter #17
Sounds like your bypass is faulty. You might try running the jumper from the battery (+) to the coil (+) again and start the engine, if it starts remove the jumper and see if it keeps running.
I ran the jumper from the battery and started the car - and the car stalls when the jumper is removed (key left "on"). So this points to my bypass wire? I'm not sure what could have changed when I only changed the coil from stock to the Flamethrower III. Could it drawn more current and exasperated a poor splice connection? Nonetheless, I can reroute the bypass but I need to know if it would be okay to tap in at the smaller gauge wire next to my resistor wire. Or what would happen if I tapped onto the resistor wire right at the ignition switch? How much resistance could there possibly be that close to the source? I'm trying to avoid pulling my dash apart............again. I'm guessing this is why some people choose the relay method.

IMG_3803.jpg
 

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I use pertronix III and flamethrower on my 69 mach1 351. I spliced a wire from ignition switched 12v directly to flamethrower. The pink wire is not connected anymore and tucked away. Obviously my Tach is disconnected as well since it is in series with pink wire. Is yours the same way? You said you bypassed pink wire so does that mean the end of it is disconnected?
 

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You know I’m sorry i may not understand your question.

I bypassed the pink wire to the positive side of the coil with the splice from red/green. Pink still goes to factory tach and works great.

I am running the 12v power from the back of the ignition switch. Ran a fresh wire with an eylet to the back of the ignition switch the lost on the back.
 
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