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Discussion Starter · #1 ·
Ok , stareing at this for a while now. Trying to " get it".

Making my own harness and was not planning on having a conventional starter relay. I was going to use a power distribution , and a mini starter instead.

Now I am an EFI guy in background and the later starter relays dont have this second pin on them where the brown coil wire plugs into.

So I see the wire starts at the ignition switch (C terminal, correct?) , then goes to the main disconnect where it splices off and goes to the coil. The other side of that splice goes to the starter relay.

I am about to elimnate the whole curcuit and tie it in with the fuel pump relay , triggered by a switch. But I would rather have the fuel pump relay an the coil work with just the key.

I guess I just need to know if its purpose of attaching to the starter relay is if the ignition switch terminal does not provide power while cranking. If not, what am I misunderstanding?
 

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I can't explain why Ford did it this way (maybe someone else can chime in), but I can tell how to make your setup work. Your setup sounds just like mine (w/ power distribution stud and PMGR mini-starter with no fenderwall starter relay). All I did was merely run a 12V switched wire to the coil - I believe from the reverse light switch connection at the firewall (but it doesn't matter as it can come from anything that is switched IIRC). The car is my daily driver, and this has worked fine with no probs whatsoever!

Good luck!
 

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DON"T run a full 12 volts to the coil! It will work for a while but it WILL burn out the coil. There is actually two circuits to deal with here, the start circuit and the run circuit. It may be a bit hard to explain but the coil is NEVER supposed to see more than about 8 volts and that is why there is a resister in the circuit, on the early Mustang that will be the soft pink wire from the ignition switch that has a warning on it not to cut. The system works like this-When you engage the starter the entire system voltage would drop down to about 8 volts or even less due to the large load imposed by the starter motor so if the coil were designed to operate on a full 12 volts it would get weak voltage and thus make a weak spark right when it needed it the most, during the start phase. To get around this problem the auto makers use a coil designed to operate on 8 volts and have a wire from the solenoid to the coil to carry full battery voltage during cranking, that is the wire that was mentioned that is missing from the newer systems. This wire then drops out of the circuit when the key is moved from "start" to "run" and the coil then is supplied with voltage from the ignition switch that first is connected to the resister (the pink wire from the switch under the dash) that will cut the voltage down to match system voltage as it is under the starter load. More simply put there must be a resister in the run circuit to drop the voltage but a wire from the solenoid to bypass the resister ONLY during cranking. The system MUST be wired in this manner because if you run a full 12 volts to the coil you will get the proper voltage while cranking but it will jump to full voltage when the starter load is released. If there is a full 12 volts supplied to the coil while running the coil will overheat and burn out before long and in fact it is not at all uncommon even for one to burst!
 

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No, it is perfectly fine to run 12V to the coil full time. The reason why it wasn't done was not to protect the coil, but to protect the points. Points easily burn out and pit quicker under a full 12V load.
 

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Sorry but it is NOT ok to run a full 12 volts to the coil all the time and even pointless ignitions do not not run full voltage so the reduction is not to protect points. The coil is wound to provide full spark at cranking voltage, which will be much lower because of starter motor load, and when this is released the voltage would go back to a full 12 volts which is too high. The resister is there to provide the proper low voltage during run and the wire from the solenoid is to bypass the resister during cranking when the system voltage is low. If using solid state controls all that will be needed is to provide 12 volt to the control circuit but NOT 12 volts directly to the coil switched or otherwise. Don't take my word for this Look at a service manual (late model solid state pointless ignition) at the ignition test procedure and see what it says about the proper primary coil voltage and what it is supposed to be, and also the steps to take if it is too low OR too high!
 

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My Still in box crate Motor has a bright orange tag on the coil instructing it to be hooked to a keyed 12 volts as MidLife stated.

I am no expert at all...but my Engine builder is pretty well known. I suppose they may be correct.

I have a resistor I took off the fender of the car and remember it being there before the coil.
But I now have No points.
 

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Discussion Starter · #7 ·
Thank you guys!

I was begining to think no one here liked me , or they were already sick of my wiring questions.

Hopefully this is the last of them.

This helps because now i know, I really dont need that whole curcuit. Its getting an aftermarket ignition, msd pro billet dist, and coil. But without understanding the old set up, i was afraid of running into issues later. I guess I am one of those people that just have to know "why".

Rorin, now you got me thinking. I was planning on pulling the reverse light wiring and the neutral safety wiring out of the fire wall, plugging the holes, and running them on the inside down to the trans tunnel to the AOD like in the late model set ups. I am trying to hide as much wiring as possible. But I never thought of it as a switched power source.
 

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Fellows do as you wish, I only explained why the factories did it they way they did (and still do). Maybe they are doing it wrong and the service manuals are wrong also, you will probably know one way or the other in a few months as that is about how long it takes.
 
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