"S" vs. "R" - the continuing starter debate - Chevelle Tech
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post #1 of 11 (permalink) Old Sep 21st, 99, 8:04 AM Thread Starter
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As recently as yesterday I read and responded to a question concerning starter wiring and the mysterious labels "S" & "R" for the terminals of the starter solenoid.

While motorcycling into manhattan this morning (in the rain) I had a flash of understanding:

The "S" terminal is the hook-up for the fat purple ignition switch lead, everyone agrees with this. But what does the "S" stand for? SOLENOID. This terminal activates the starter's solenoid.

The "R" terminal is hooked up to a yellow wire which leads to the coil, which supplies additional battery voltage to the coil ONLY WHEN THE STARTER IS TURNING. This is important, because it tells us what the label "R" means. The "R" terminal is a RELAY terminal, which is switched on and off by another circuit.

I haven't got documented evidence that these lables are correct, but they make a lot more logical sense than some of the other ideas that were floated in a previous post. And with this system of labeling one can actually remember what goes where and why.

Please, if I'm in err please let me know.

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post #2 of 11 (permalink) Old Sep 21st, 99, 2:11 PM
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I thought S was for Switch and R for Relay

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post #3 of 11 (permalink) Old Sep 21st, 99, 2:53 PM
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I believe it is R esistor because the yellow wire is a resistor wire to coil on stock ignitions. Of course I may be mistaken

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post #4 of 11 (permalink) Old Sep 21st, 99, 3:01 PM
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The S on the solenoid stands for START which is what the purple wire is for...it activates the solenoid when you turn the ignition switch to the start position. The R terminal stands for RUN and what the yellow wire does is send 12V to the coil for start up because as soon as you release the key in the ignition switch, that circuit shuts off and the coil is fed through the resistor from the ignition switch.

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post #5 of 11 (permalink) Old Sep 21st, 99, 4:40 PM
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Talk about confusing. Sport Truck magazine has a tips section and they show a picture of the typical solenoid with the info that you can renew the solenoid just by swapping places with these two wires. I'm no expert, but I think the proofreader was asleep that day. tom
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post #6 of 11 (permalink) Old Sep 21st, 99, 5:18 PM
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michael j gets my vote

Why would "R" be for run when it is only used during cranking and it is from the relay.
"S" is what powers the solenoid so that makes sense too.
The yellow by pass wire is not a restive wire so the "R" can't be for resistor.

makes sense to me

Is there an "S" on the back of the ignition switch where the purple solenoid wire attaches ?

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post #7 of 11 (permalink) Old Sep 11th, 03, 6:32 PM
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Well here's my two cents. I guess I always thought that "S" would mean solenoid or hot starter wire from the the ignition switch. The "R" ,for some reason, sticks in my mind as a type of resistance connection. Bottom line in my way of thinking, when the ignition switch is used all the available battery voltage is deverted to the starter and the "R" terminal prevents the voltage from going to any user i.e. radio, heater fan etc. until the car is started or the ignition switch is de-energized.
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post #8 of 11 (permalink) Old Sep 11th, 03, 7:04 PM
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Ok, I did a litte checking on the R/S thing. I wasn't totally correct in my above statement. Imagine that!! Here's the scoop as the mighty book says. The infamous "R" terminal is attached to a metal finger which makes contact with a disc inside the solenoid when it is energized. This terminal is connected to the battery side of the ignition coil. The purpose of this terminal is to "short" out the ignition resistor during cranking and thereby provide high ignition coil output for starting the engine. Sorry if I mislead anyone.
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post #9 of 11 (permalink) Old Sep 13th, 03, 10:38 AM
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It doesn't short out the resistor wire it bypasses it to give higher voltage to the ign coil. When the starter engages it drops the battery voltage to approx 10.5 - 11 volts (batteries of 30 years ago were no where close to the technology of today and may have even dropped lower). Going thru the resistor wire the spark would be to weak to fire the plugs well enough to start under some conditions, like cold winter weather. Sending the available battery voltage to the coil while starting boosted the output of the coil allowing for easier starting.

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post #10 of 11 (permalink) Old Oct 2nd, 03, 8:26 AM
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S = switch
R = resistor

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post #11 of 11 (permalink) Old Mar 24th, 04, 11:34 PM
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My .02
S=Start or solenoid, I think start
R=relay provides voltage only when energised.
On a related topic there are two windings in the
solenoid the "Pull in" and the "Hold in" windiings. The Pull in is wired between the S and the big starter terminal. Current would flow until the solenoid engauges. The hold in winding goes between S and ground and always draws current. Therefore the solenoid current should be <15A when first energised and should drop down to ~5a once engauged.

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