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Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 06-10-2009   #1 (permalink)
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Default "I" TERMINAL on Starter Solenoid?

What is the "I" terminals purpose on the Starter solenoid? Also, if I disconnect all the wires to this "I" terminal and the car is in the "start" position am I right to assume that this terminal should show 12 volts at the terminal itself and then will read 0 volts once the key is in the "run" position? I have an HEI system with a 12v separate coil so do I even need to use the "I" terminal on the starter at all or can I run a straight keyed on power wire to the + side of the coil instead?

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Unread 06-10-2009   #2 (permalink)
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If I'm following you correctly, you will still need power from the "I" post to your ignition switch in order to transfer power to the starter when cranking to start. That's its primary purpose.
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Unread 06-10-2009   #3 (permalink)
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If that wire to the terminal is hot all the time the starter will keep trying to start the motor. That is your momentary switch for the hi amps that flow through to the starter.
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Unread 06-10-2009   #4 (permalink)
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The I terminal stands for Ignition

The purpose of it to supply 12 volts to the coil during CRANKING the starter bypassing the ignition switch which has a resistance wire running from the switch to the + terminal of the coil

There should NOT be power at the I terminal when the engine is running.
You see Ford coils run with 7-9 volts not 12v

A constant 12 volts would burn the coil up
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"I" TERMINAL on Starter Solenoid?-73_74pointignition.jpg  
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Unread 06-10-2009   #5 (permalink)
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Quote:
Originally Posted by MIL1ION View Post
The I terminal stands for Ignition

The purpose of it to supply 12 volts to the coil during CRANKING the starter bypassing the ignition switch which has a resistance wire running from the switch to the + terminal of the coil

There should NOT be power at the I terminal when the engine is running.
You see Ford coils run with 7-9 volts not 12v

A constant 12 volts would burn the coil up
OK Now I think I understand what is going on. On a conventional POINTS type ignition system the coil needs 12v at startup and then requires 7-9 volts after the car starts to run properly. So the wire running from the ignition switch is a two part wire, one part runs to the + side of the coil with a resistor in between to provide the + side with 7-9 volts when the car is running the other comes off of the I terminal and is a direct wire to the + side of the coil providing 12 volts while the engine is cranking only.

Two things though. One... I have a 12 v HEI ignition system with a coil that is a breakerless 12v coil which I assume needs 12 v all the time. The way my I terminal is hooked up is this way. It has a KEYED 12 volt wire running to the I terminal from the ignition switch which is hot when the car is in the run position. Also attached to this I terminal is a white wire that runs directly to the + side of the 12 v coil. Also, the I terminal has a red wire marked 12v running to the electric fan.. so I am assuming that whoever had this car before is using the I terminal as a mating point for the + side of the coil and as a point for the electric fan to draw its power from. The hot wire from the ignition switch is feeding power to both of these wires ONLY when the ignition switch is in the run position. When the ignition switch is in the start position(cranking) then the hot wire from the run position is dead and power is being feed to the coil and the fan via the charge through the "I" terminal. Damn I hope I am making sense....

Anyways if someone can verify what I just said that would be great. Either way I am thinking I can just bypass the whole "I" terminal all together and run a 12 v ignition switch wire to the + side of my 12 v coil and run my fan off of another 12 v source as well. What do you think?

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Unread 06-10-2009   #6 (permalink)
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"When the ignition switch is in the start position (cranking) then the hot wire from the run position is dead"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Hmm No Power from the switch runs to the I terminal in START....It is activated in the starter relay.... then no power to the coil from the I terminal once the key goes to RUN.
There should be power through the resistance wire to the coil as well in Start position

If it was me I would install a Keyed power bar on the fender rather than using the I terminal as a mating point.

Keyed power connection can be found near the Fuse box.

Please be specific with the terminology of the I circuit
The "terminal" is on the Relay.. the CONNECTOR that goes to the I terminal is part of the harness
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Unread 06-10-2009   #7 (permalink)
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Quote:
Originally Posted by MIL1ION View Post
"When the ignition switch is in the start position (cranking) then the hot wire from the run position is dead"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Hmm No Power from the switch runs to the I terminal in START....It is activated in the starter relay.... then no power to the coil from the I terminal once the key goes to RUN.
There should be power through the resistance wire to the coil as well in Start position

If it was me I would install a Keyed power bar on the fender rather than using the I terminal as a mating point.

Keyed power connection can be found near the Fuse box.

Please be specific with the terminology of the I circuit
The "terminal" is on the Relay.. the CONNECTOR that goes to the I terminal is part of the harness
OK... So one thing I should add here. The car is equipt with a Painless Wiring kit so the stock wiring harness for the most part is long gone. Funny you should mention the Keyed power bar. I was planning on getting one and using that instead. I am assuming if I am to use that Keyed power bar then I should wire a keyed 12 volt wire TO the bar and then run anything that requires a 12 volt keyed power source (my electric fan and my 12 v coil, aftermarket gauges etc..) FROM the bar? If so where is the best place to mount the bar And if I do this should I put a fuse somewhere in between for protection? If so where should I put it and how big of a fuse should I use??

Thanks again for all the help I really appreciate it.

Mark
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Unread 06-10-2009   #8 (permalink)
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i went with an msd 6al box and the way i wired it is the the heavy red to battery positive and the black to ground. Then you have the pigtail usually a purple and a green wire to the distributor, and an orange and black wire for coil. And the original wire that went to coil positive you use for the ignition on power source. If you followed that wire back to the firewall it splits to the brown wire for the starter solenoid "I" you want to remove this wire from the solenoid because it kicks the voltage down for the points ignition, and your hei system probably wont work with it.
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Unread 06-11-2009   #9 (permalink)
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When the key is in the "start" position the only wire that has power from the ignition switch is the wire to the small "S" terminal on the starter solenoid. When power is applied to the "S" terminal, the starter solenoid closes. When closed the large terminal to the starter and the "I" terminal to the coil gets power. There is no other power going to the coil.

When the ign. switch is shifted to the "Run" position there is no longer power to the "S" or the "I" terminals and the solenoid is now open and the starter is also no longer cranking. Power to the coil has now shifted, through the ign. sw. to the wire that contains the resistor wire.

The coil wire has a splice in it. From the coil, one end goes to the "I" terminal and one end comes from the ign. sw. with the resistor wire. When in the "Start" position power can only go to the coil from "I" because the ignition switch side with the resistor wire is open and the solenoid is closed. When the ign. sw. is in the "Run" position, power can only go to the coil from the now closed ign. sw. because the solenoid and the "I" terminal is now open.
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Unread 06-11-2009   #10 (permalink)
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So if I have this right then this is the way it works.... Two wires are coming off the Ignition switch. One runs from the START position to the S terminal on the solenoid, the other one runs from the RUN position of the ignition switch to the + side of the coil. THEN from the Solenoid itself you should have one wire coming from the I terminal to the + side of the coil. This way the coil has power going to it from the Start position (Run position dead, solenoid closed powering the starter and the I terminal, sending power through the wire to the + side of the coil) And from the RUN position( start position dead, wire directly from the ignition switch to the + side of the coil) Thank you for clarifying this for me. I understand what this guy did now. This is what he did.

On the I terminal of the solenoid he has three wires.... One is a wire coming from the RUN position of the ignition switch, One is a wire that goes to the electric fan(supplying power to it), and One is going to the +side of the coil... Upon startup the first wire (one from Run position) is dead but the I terminal is powered because the car is in the START position. Once the key goes into the RUN position the I terminal is not powered naturally but is now powered by the START wire, powering the fan and continuing to power the wire going to the + side of the coil. Like I said before I think this guy was trying to find a way to power the fan and is using the I terminal on the solenoid to do it. It is a creative way but I dont like it. I would rather wire it the right way and use a 12 v Keyed power bar to run power to the things that need it now and in the future.

Sorry so long but this is the only way I can get it all out of my head and in a format that I can go back to and look at it. THANKS AGAIN I KNEW US GREEKS WERE SMART!! LOL!!:hihi:
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