Please continue to comment. I feel I am somewhat experienced, but have got lost a bit in all the knowledge. I have the non-tach car wiring figured out I think. Simply put, you need a “keyed” 12 volt source to the Pertronix red wire. The black wire from the Petronix goes to the negative side of the coil. The resisted power wire goes to the positive side of the coil as stock.
I think I understand that if you do not power the Pertronix and the coil from the same stock coil power source (the resisted wire) wire that the tach will not work? So you either “splice” into the keyed stock power wire to the coil before the resisted portion of the stock power wire. Near the switch or in the harness before the resisted portion. OR you get the relay to allow the ability to splice in in the engine compartment area.
I should have used some question marks above, but I hope I have it correct.
Pertronix relay instructions https://static.speedwaymotors.com/pdf/4472001.pdf I conetted the power from the battery side of the solenoid. Just follow the instruction and you will done in about an hour.
You have the non tach version down. The cool part is that it is the same way you wire the tach version. All you are doing is providing a 12 volt source to the Ignitor. The coil positive stays hooked up to the same stock power wire. You can get that 12 volts source two different ways: run a new wire from the back side of the key switch, or use the Pedapter under the hood, wired according to the Pedapter instructions.
As long as you don’t have a stock tach, and use a coil that does not require a ballast resistor, this will work. It also allows you to connect the Ignitor red wire to the positive post of the coil because it is getting 12 volts. If you do have a stock tach (XR-7) the tach will not work.
Something that may be getting lost in all of this is that there are two independent circuits involved in the discussion: power to the Ignitor, and power to the coil.
Power to the Ignitor
All of the Ignitors are designed to run on 12 volts. The power wire that goes to the coil ISN’T a 12 volt source on ANY stock Cougar. So you either run a new wire from a 12 volt source that is ONLY hot when the engine is cranking or the key is in the run position. That can be found at the back side of the key switch.
Power to the Coil
The stock coil is designed to run on 12 volts only for very short periods of time: specifically when the starter is cranking. A resistor wire that is located under the dash, drops the voltage to the coil to about 6 or 7 volts. Some aftermarket coils are designed to run at 12 to 14.6 volts all the time. They also pull a lot more current. The possible advantage of an aftermarket coil is that it can deliver a higher voltage to the spark plugs. There are two serious considerations when using an aftermarket 12 volt coil. 1. The factory tach is a part of the circuit that feeds the stock coil. It is not compatible with 12 volt coils. 2. The contacts in the ignition key switch are rated for about 8 amps of current. a 12 volt coil will exceed that rating. This will require the use of a relay to provide the higher current the coil will require.
Thanks Bill! So if I provide a 12 volt source from a “keyed” fuse in the fuse block will the stock tach still work? By tapping into the ignition switch area you still have the ignitor itself tied to the power through the stock tach. My guess is that the 12 volts source from the fuse block will not operate the stock tach?
Sorry for one last question, but I am gaining a lot of knowledge on this subject. This will allow me to run an Ignitor I with a stock Ford coil. I have two current applications (the Mecum Red GTE and a 68 Shelby) that will benefit from this discussion.
The stock tach will work with the Ignitor as long as you use a stock coil with stock wiring to the coil.
You can feed the Ignitor with 12V from any start/run source.
The factory wire AT THE COIL is NOT providing 12V when the engine is running because the coil is after the pink resistor wire.
But, as long as your 12V feed wire is connected to that wire BEFORE the resistor you will have 12V in start and run. This requires finding the correct wire under the dash BEFORE the resistor wire.
The easiest/cleanest way to get 12V under the hood is with a relay. That relay will have to be activated by a start/run power source. There is no OEM start/run 12V power lead under the hood on our cars so we use the only one we have to activate the relay and the battery to provide the 12V.
The only issue is when folks want to run a new 12V feed to a high performance 12V coil.
Bill is correct - part of the confusion is that there are TWO circuits involved, power to the coil and power to the igniter. The Pertronix Flame Thrower coil needs twelve volts.
So - you can run your own wire and tap into a 12v source before the pink resistor wire. That’s doable, but looks like a lot of work and acrobatic body positions.
Or - you can get a relay from RCC or Pertronix for about $40. Much easier install.
For the Pertronix, you can get your 12v from the starter relay. That 12v source makes its way to the coil by connecting the relays purple wire to the ignition red wire which went to the coil. That connection turns into an orange wire out of the relay and connects to the + side of the coil. So, there’s your 12v to the coil. The igniter red wire also goes to the + side of the coil, so 12v to the igniter. Black wire from the igniter to the - side of the coil.
I think RCC’s is similar. The difference being the P001 is switchable 9v or 12v to the coil. The P002 is a constant 9v.
Fellas - I just measured voltage off the I post of the starter relay with the car running. I only recorded 8.25 volts.
I’m going to assume for the power relay I need 12 volts. Should I have around 12 volts at the I side or the starter relay with the car running? Starter relay going bad? Thx
During START you will have 12V or more. The 12V will activate a relay.
Once running that post will only have ballasted voltage but it’s enough to hold the relay closed.
The I post ‘bypasses’ the resistor wire and delivers full battery voltage to the coil during starting. If it didn’t do this the coil would get extremely low voltage due to the drag of the starter and the resistor wire.
Ford vehicles with electronic ignition do not have the I post on the solenoid because they don’t have a ballast resistor.
During start, I only have about 10v at the I post. My battery is in great shape. So maybe a failing starter relay?
I only have about 8v at the I post in “run”. So that is my ballasted voltage. But I thought both power relays were designed to tap into a 12v source? Isn’t that what the Pedaptor is designed to do? 12v during start and run?
Let me try to explain a relay. Inside the relay is a coil and a set of open contacts, one side of the coil is hooked to the I terminal on the starter relay and the other to ground, the red hot wire from the battery connects to one side of open contacts, the other side of same relay goes to the igniter . When the key is turned to start, voltage from I terminal flows through coil which causes the open contacts to close and pass 12 volt to igniter.
When you turn key off that kills power to rely and the contacts open and kills power to igniter.
The overthinking is due to conflicting information between magazine articles, power relay install instructions, and this twelve page discussion.
I have seen three sources of 12v quoted - I terminal of the starter relay; batt side of the starter relay; and the positive battery post. And, on my car, NONE of those sources deliver 12v. I get 8v from the I terminal in run and 10v in start. For the batt side or positive post, I have over 14v in run. Unless the two power relays discussed somehow convert that into 12v, I don’t have the “12v” source.
Connecting the power relay to the ignition offers three options - positive side of the coil, igniter, or electric choke.
So - I’m not sure “overthinking” is accurate. Especially in this case, with voltage, current and amperage involved. Nobody wants to do it wrong and burn something up.
But I also have appreciated the discussion and patience of the subject matter experts here.
All this has been explained ad nauseam in this thread.
The I terminal of the solenoid = Battery voltage during START. Unless you have a starter motor with 0 resistance you are going to see a voltage drop. This voltage drop is why Ford added the bypass wire (the little wire on the I post) to bypass the resistor wire. Without the bypass wire you would have about 5V to the coil during start.
Battery side of the solenoid and positive post of the battery ARE THE SAME THING! LOOK at the wiring - Battery positive post to Solenoid post. Nothing between the two posts to make them different.
You want technical? Fine.
The CORRECT term for battery voltage in a ‘12V’ system is B+. B+ is the actual battery voltage at the positive battery terminal. The reason engineers use ‘12V’ or ‘power’ instead of B+ is because 99% of the guys actually working on cars know that they have either a 6V or 12V system.
Unless you have no working charging system and no electrical load B+ will fluctuate as the charging system works and loads increase or decrease. B+ during starting may be only 10V. During a 2000 RPM cruise it may be 14V. Good luck finding a connection anywhere on your car that is 12V all the time.
Magazine articles, and manufacturer’s write ups may differ depending on what they’re trying to sell, but physics don’t. So here it is in a nutshell with no variables:
Points will burn up with B+, breakerless ignition modules want B+.
Ignition coils made to run on ballasted voltage will overheat and fail when B+ is supplied for extended periods.
Yes, even I understand that the positive post of the battery is the same as the BATT side of the starter relay, in volts.
I also see, at least on my car assuming my starter relay is in good shape - those two sources of voltage from the battery are NOT the same as volts from the I terminal of the starter relay. On my car, in the run position, it is the difference between 14+v and 8+v. That’s quite a big difference.
I’m not arguing with anyone. I’m just asking questions to gain knowledge. I’m not a mechanic. I’m an airline pilot, but I have been working on my car for over forty years. I have some skills, but obviously not at your level.
Again Bob, thanks for the discussion. Your tach continues to work well.
Yes, you have ballasted voltage at the I post when the engine is running. That is how the system works.
Here’s how the coil gets it’s power:
The ignition wire goes from the ignition switch through the ‘pink’ resistor wire, through the firewall to a junction with another ‘hero’ (also called a bypass) wire, then on to the coil + side. Pretty basic, right? Key ON = Power to coil = car runs.
But what about the key in START? You have the same wire feeding the coil. Problem is, the starter is pulling A LOT of voltage and that darned resistor wire is only letting about half of those volts get to the coil. So instead of the coil giving out a manly beer BURP, it gives a Victorian debutante closed mouth behind the hand burp and the plugs go yawn.
When the key is in START position it sends B+ to the solenoid S post. This energizes the solenoid so both big posts (Battery & Starter) and the small I post are connected together. The starter and the I post get B+. A quick note about the I post: It’s purpose is to SEND voltage out. The I post is normally unpowered.
This is where our hero wire comes in. That hero wire sends B+ from the solenoid I post to the junction up by the firewall (after the resistor wire) down to the coil. The coil lets out a Booger style spark and viola! the engine starts. Release the key and the coil input is reduced to roughly 1/2 of B+ or BV (Ballasted Voltage).
Think of electricity in wires like you would water in pipes. That electricity wants to get to ground and it’s looking everywhere for a way out, much like water in a pipe. That hero wire is no different. Now that there’s no B+ flowing up it from the I post the BV (ballasted voltage) from the pink wire goes rushing down it looking for a way out. But when it gets to the solenoid there’s no where to go. That’s why your I post is about 8V. It’s supposed to be.
So now you have basically a Y shaped wire full of BV with the resistor wire feeding the two arms. The one going to the coil keeps the coil sparking and the one going to the I post isn’t doing anything. But… we can use it to trigger, or turn on, a relay. As long as the key is on the relay will remain closed.
Remember that B+ jolt during start? Just like it’s enough to fire the coil, it’s enough to close the relay. Just as BV is enough to fire the coil, BV is enough to ‘hold’ the relay closed.
In other words, the I post during run has the same voltage during run as the coil does - just like your bathroom sink has the same water pressure as your kitchen sink. The difference is when you flush the toilet our hero pipe ups the water pressure you you don’t get scalded in the shower.
to the solenoid S post. This energizes the solenoid so both big posts (Battery & Starter) and the small I post are connected together. The starter and the I post get B+. A quick note about the I post: It’s purpose is to SEND voltage out. The I post is normally unpowered.