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Pertronix Coil and Ignition Conversion Made Easy
In order to provide a constant 12 v source to the Pertronix Ignitor coil that is only powered when the ignition switch is in the run position, you will have to tap into the wire on Terminal C of the ignition switch. The hardest part is taking the ignition switch out. First, disconnect your battery to be safe. Next, see if you can get your hand up there and push it forward. If not, you can then use a very large screwdriver to get behind it and pry it forward. There is a hefty spring that holds it tight. Take note that the bezel comes off with a counter-‐clockwise twist-‐-‐ when you are removing the bezel you have to push it in while turning it counter-‐clockwise. You will then see that the bezel was held on with a large pin on the left and a smaller one on the right. You have to line up the larger pin with a slot at 9 o’clock in the sheet metal to pull the switch out. The wires will be short but workable. If you use the Pertronix Flamethrower instead of the original coil you want 12V going to it since it has internal 1.5 ohm resistance. Find the wire on the ignition switch that is the only one in the ON position and not ACC. It is the normally the red wire with a green tracer. You have to tap into the pigtail before the resistance wire shown at C in the wiring diagram. The resistance wire portion is pink on most wiring diagrams and connects to the red/green wire coming off Terminal C with a black butt connector. You can tap into that with a vampire tap and run a wire from there along the hood release cable and attach it with black wire ties. You can then just disconnect the resistance wire. If you have an electric choke on your carburetor you can make a separate wire with another ring terminal on it and run it from the coil to the carb.
Here is my old pigtail. You can see there is a red wire and what appears to be a red-‐green wire with the butt connector. That’s the one you want to tap into before that connector.
Here is a closer view of the wire showing the green stripe. Mine is slightly melted which is why I replaced the pigtail.
Here is my new wiring job. It’s hard to see the colors but the new pigtail has the red-‐green wire for the resistance wire and they labeled the starter wire red-‐blue, which is the alternate color in the wiring diagram. You can see in my photos that I have replaced my pigtail with some modifications to give me a lot of slack. Just to be safe, I put a blade type inline fuse holder in which is the heavy gauge yellow on the left (that’s all I could find, 30A or something) and that goes to the black wire that I ran to the coil. I think I put a 3A or 5A fuse in it. The yellow wire on the switch is power in. Since that constantly hot, I spliced into it for the clock for the Custom Autosound radio.
Here is the abandoned resistance wire. It has a plastic-‐like coating on the insulation and is somewhat pink and is labeled “resistance”. I think it was probably smoked so I don’t think there is resistance in it anymore. As you can see the insulation is falling off, probably from being cooked.
So just to be sure I did some tests with the ohm meter. Here is the resistance wire with the switch in the ON position. So there is full conductivity there. I tested in ACC also and it is off. The lock is worn out on this switch so I had to keep jimmying the key around to get it to move.
Moving over to the red starter wire, here is the switch in the ON position, no conductivity.
I made sure it had conductivity in the START position.
Notice S on the diagram above is red or red-‐blue. That wire goes to the starter relay and is only on in the START position. You don’t want to tap into that one. The other wire that is not color labeled at C is red-‐green. That is the only wire that is on in the ON position. There is a butt connector attached to it and beyond that it turns into the pink resistance wire. It looks long but as you’ll see in the next photo, it is short. You want to tap into that before the resistance wire. In the end you will have three wires on the (+) side of the coil-‐-‐ the new 12V in you just added, the Pertronix module, and the optional wire going to the carb electric choke. If you find they interfere, you can remove the plastic insulators on the ring terminals, solder them and put shrink tubing on them so you won't have any problem fitting the three lugs on the coil. The Pertronix Ignitor unit, use the Hall Effect to magnetically trigger some electronics. In the Ignitor, the connection to (+) simply provides power to the unit. Then there are probably some transistors that quickly switch the power on and off to the coil, again by controlling the circuit to ground. The induced back current can be easily handled by some hefty diodes. These things are just a win-‐win in all respects. The reason the points system only had a wire from the (-‐) side of the coil to the distributor is because the points are on the ground side of the coil. In the old system, 9V was provided to the coil (+) by the resistance wire. The wire from the (-‐) side of the coil went to the points. When the points were closed, voltage flowed from (+) through the primary windings and out (-‐) to ground through the points that were ground through the whole distributor. When the cam came along and opened the points, the field collapsed generating the high voltage on the secondary side of the coil. Now, during this collapse the secondary windings induce a small “back current” in the primary windings, which tries to seek ground and causes arcing across the points when they are open. This enters the condenser, which buffers that back current and reduces arcing across the points. Here’s a great diagram. This is exactly the Ford setup. Here it is easy to visualize the condenser as the reverse induction spark suppressor when the points are open. The primary and secondary windings share a common ground inside the coil.
I thought it would be interesting to trace out the brown wire circuit. I captured the top and the bottom of the diagram leaving the unnecessary stuff in the middle out. If you look carefully at the diagram below, you will see that the resistance wire splits after the firewall, with one branch turning into a brown wire that goes to the starter relay. I did some research on this-‐-‐ there are two wires on the relay, one labeled S and one labeled I. Most starter relays that I have seen only have S. “I” provides a full 12V from the starter relay to the coil during ignition, (thus the “I”). This gives the coil a boost during starting. Once the relay is released, the voltage drops back down to 8 or 9 to the coil. This will become a moot point after you run your 12V line.
So now it’s easy to see how the circuit works. When the starter relay is activated, 12V goes out the brown wire and hits the resistance wire. Since the coil is most likely the path of least resistance, it brings it up to 12V during starting. I thought this was pretty cool. Take a look at my video: http://www.youtube.com/watch?v=v_bCX7FrUrI&feature=youtu.be on this issue.