"I" and "S" terminals on Solenoid - Vintage Mustang Forums
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post #1 of 19 (permalink) Old 03-21-2009, 09:32 PM Thread Starter
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"I" and "S" terminals on Solenoid

What exactly are the "I" and the "S" terminals on the solenoid for?


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post #2 of 19 (permalink) Old 03-21-2009, 10:06 PM
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"I" and "S" terminals on Solenoid

When you turn the key to start... power runs from the ign switch thru the NSS to the S terminal of the solenoid causing a high amperage of power to travel from the battery to the starter lug of the relay to the starter to crank the engine ....at the same time while the the key is in Start, power (12 Volts) from the I terminal runs to the coil for easier starting.
Once the key return to RUN ..7-9 volts is delivered to the coil operating the ign system

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post #3 of 19 (permalink) Old 03-22-2009, 12:09 AM
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That's pretty much the way it works. To add to the description of the 'I' terminal, it supplies the full voltage to the coil which is otherwise reduced by the pink resistor wire.

I always assumed 'S' indicated starter and 'I' indicated ignition.
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post #4 of 19 (permalink) Old 03-22-2009, 03:38 AM
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Those terminals have always puzzled me. When I got my car, the solenoid only had one of those terminals and there was no extra wire I could find to indicate I should have had both terminals. When I replaced the solenoid, the new one had both. When I replaced the wiring harness, it had a wire for each terminal. I hooked them both up, but I'm not really sure if it did anything.

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post #5 of 19 (permalink) Old 03-22-2009, 06:46 AM
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I'm pretty sure Ford quit using the I teminal when they went to electronic ignition. All points ignition cars should use the I terminal.

Joe

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post #6 of 19 (permalink) Old 03-22-2009, 02:19 PM
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The difference was the vehicle and the main harness
whether the Ignition by pass wires was used.
Mopar used a Ballast resistor(white porcelin Block with resistor built into it) for years.





in the 80's they changed back to this design.

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post #7 of 19 (permalink) Old 06-14-2009, 08:33 PM Thread Starter
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So... if I am running an MSD electronic distributer and an MSD 6AL box, do I need to connect the "I" terminal?

Tim

'65 2+2
347 - Holley DP - 471 fwhp
JBA shorty's, 2.5" tubes, Dr Gas X-pipe
T-5 world class 5 speed, w/ .80 OD
9" with 3.70's & T-loc
4 wheel Wilwood disc brakes
17" CL-205's, 225/45 & 255/40
TCP/Global West suspension
OpenTracker roller spring perches
subframe connectors, Panhard bar
TCP manual rack & pinion
Power door/window locks w/ keyless entry
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post #8 of 19 (permalink) Old 06-14-2009, 08:54 PM
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Quote:
Originally Posted by Tims65
So... if I am running an MSD electronic distributer and an MSD 6AL box, do I need to connect the "I" terminal?

Tim
My only question is: was the resistance wire (original ford coil power wire) used to power the new ign system? if so, it not getting proper voltage. If not, the I terminal is most likely going to a dead end wire

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post #9 of 19 (permalink) Old 06-14-2009, 09:54 PM
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Tim, the answer to your question is no it doesn't need to be hooked up. Brian brings up a good question though. How did you hook up your box? If you used the power lead for the old coil hook-up, you are running low voltage to the msd box. If you unplug the pink wire under the dash and plug a new wire into the lead that the pink was plugged into, run that new wire to the msd box.

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post #10 of 19 (permalink) Old 06-15-2009, 09:11 AM Thread Starter
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Sorry guys, I'm still a little confused.

I'm currently rewiring my engine compartment and trying to hide all of the wires. I'm trying to decide if I should relocate the solenoid or if I can eliminate it. I have one of the new high torque mini starters, but it does not have a provision for the "I" terminal. I do have an electronic MSD distributer and MSD-6AL box (I have not wired them yet).

Please provide me with your knowledge!!

Tim

'65 2+2
347 - Holley DP - 471 fwhp
JBA shorty's, 2.5" tubes, Dr Gas X-pipe
T-5 world class 5 speed, w/ .80 OD
9" with 3.70's & T-loc
4 wheel Wilwood disc brakes
17" CL-205's, 225/45 & 255/40
TCP/Global West suspension
OpenTracker roller spring perches
subframe connectors, Panhard bar
TCP manual rack & pinion
Power door/window locks w/ keyless entry
Driven, not pampered
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post #11 of 19 (permalink) Old 06-15-2009, 06:40 PM
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Does the MSD box run on 12 volts ?

The I terminal was just used to send 12 volts to the coil during starter cranking.

If the MSD box runs on 12 volts and you have a 12 volt source to the coil when you crank the starter and RUN ,then NO ,you don't need the I terminal or bypass circuit
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post #12 of 19 (permalink) Old 06-15-2009, 09:25 PM Thread Starter
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Quote:
Originally Posted by Mil1ion
Does the MSD box run on 12 volts ?

The I terminal was just used to send 12 volts to the coil during starter cranking.

If the MSD box runs on 12 volts and you have a 12 volt source to the coil when you crank the starter and RUN ,then NO ,you don't need the I terminal or bypass circuit
Yes, the MSD-6AL box uses a 12 volt constant hot and a 12 volt switched hot.

So is the lead that connects to the "I" terminal a 12 volt switched (ignition hot) power source?

Tim

'65 2+2
347 - Holley DP - 471 fwhp
JBA shorty's, 2.5" tubes, Dr Gas X-pipe
T-5 world class 5 speed, w/ .80 OD
9" with 3.70's & T-loc
4 wheel Wilwood disc brakes
17" CL-205's, 225/45 & 255/40
TCP/Global West suspension
OpenTracker roller spring perches
subframe connectors, Panhard bar
TCP manual rack & pinion
Power door/window locks w/ keyless entry
Driven, not pampered
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post #13 of 19 (permalink) Old 06-20-2010, 01:14 AM
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Pertronix Flamethrower Coil and "I" terminal

Some great info on this thread. Been wondering what the I terminal was for for awhile now. Now, time for my question:

I'm installing a Pertronix Flamethrower Coil (built-in 1.5 Ohm resistance) on my 302. I have removed the resistance wire, and am wondering if I should remove the connection at the I terminal as well. Since the resistane is now internal to the coil, the 12 volts that comes from the I terminal will now be stepped-down. Thus, don't see any reason to include.

Any thoughts?
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post #14 of 19 (permalink) Old 06-20-2010, 01:47 AM
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Not to add any confusion, but all coils have resistance in the primary windings. Stock coils are 1.4 ohms. The 1.5 ohms of the Flamethrower coil, for all practical purposes, doesn't change anything. (Being that it's only a 0.1 ohm difference.)

That being said, if you have bypassed the resister wire, the wire to the "I" terminal no longer serves a purpose, as there is no longer a resistance wire to bypass during starting. Whether you leave the wire there or not is personal preference - it doesn't do anything anymore, but it won't hurt anything, either.

I would not remove the resister wire if you are using points, or they won't last very long. At all.

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Last edited by Joe; 06-20-2010 at 01:53 AM. Reason: more
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post #15 of 19 (permalink) Old 06-20-2010, 02:20 AM
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Quote:
Originally Posted by Joe View Post
Not to add any confusion, but all coils have resistance in the primary windings. Stock coils are 1.4 ohms. The 1.5 ohms of the Flamethrower coil, for all practical purposes, doesn't change anything. (Being that it's only a 0.1 ohm difference.)

That being said, if you have bypassed the resister wire, the wire to the "I" terminal no longer serves a purpose, as there is no longer a resistance wire to bypass during starting. Whether you leave the wire there or not is personal preference - it doesn't do anything anymore, but it won't hurt anything, either.

I would not remove the resister wire if you are using points, or they won't last very long. At all.
Gotcha, thanks for the reply. I'll go ahead and keep it. I'm actually using the Pertronix Ignitor, so I've done away with points.
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