To answer the implied Question in the Thread Title about "
Whether the "Purple Wire" goes to the Starter ...or Not ...?' begs for a Complete Technical Explanation:
The Purple Wire is part of the Very Robust Relay System built into the Solenoid to avoid the need of applying -=
ALL=- of the Battery's ENORMOUS CCA (Cold Cranking Amperage) anywhere within the light 16 AWG to 18 AWG Automotive Starter Circuit Electrical Wiring that begins with the Turn of The Ignition Key inside of the Ignition Switch and ends at the point where the Lower Amperage 12 Volts DC surging down that Purple Wire induces the Coil Windings inside of the Solenoid to temporarily create a Very Strong Electro-Magnetic Field with sufficient enough PULL on the Iron Core Rod inside of the Sturdy Relay and draw together some Very Thick Copper Relay Contacts hidden inside to momentarily complete the electrical circuit.
When the Battery is Low On Charge... the only thing the Solenoid can do is to go,
*Click, Click , Click* while it is unable to make the Coil Windings create a Strong Enough, Temporary Electro-Magnetic Field and Tug on the Iron Rod hard enough to Close the Thick Copper Contacts and complete the other High Amperage side of this Electrical Circuit.
As a Temporary, but VERY STRONG Magnet, that Iron Rod momentarily PULLS VERY HARD against the Internal Spring that normally Keeps the Starter Motor Circuit OPEN inside of the Solenoid and manages to draw together some Very Thick Copper Relay Contacts capable of handling High Amperage on the other side of the Relay.
That HUGE Immediate Current Flow remains active only as long as the "Key Is In The Run Position" and held there until released and the Running Engine takes over the job of keeping the Flex-Plate Turning from then on. The Starter Relay only remains active as long as 12 Volts DC is travelling down that Purple Wire to Ground inside of the Solenoid.
Once that Robust, Thick Copper Relay Connection makes direct contact at the end of the Solenoid, this allows -=
ALL=- of the available CCA Electrical Potential inside of the Battery to surge on through with enough Heavy Electrical Pressure (Current) from the Battery Positive Terminal... Through the THICK RED COPPER CABLE directly into the Starter Motor Copper Windings and this allows the Starter Motor to Spin Over.
Once the Key is Relaxed... that Iron Rod Loses its Strong Magnetic Power and the Internal Solenoid Spring takes over and pulls that Iron Rod OUT
... Breaking the High Amperage Circuit... when those Thick Copper Relay Contacts come completely apart and remains separated until the Ignition Key is once again Twisted to the RUN Position and once again... engages the Solenoid to actuate the Starter.
Ergo... a
-=A Small, (Thin Purple Wire) Electrical Force=- ...controls a -
=BIG (Thick Red Copper Cable) Electrical Force=- and avoids the Danger of having any Uncontrolled High Amperage Current melting everything down into a puddle in between.
The necessity of using the Ignition Key to actuate Starter Motor action can actually be
--==completely side-stepped==-- by The Cautious Mechanic by using THIS (KOEO ) By-Pass Device for Solo Repairs and Diagnostics... such as whenever performing Wet & Dry Cylinder Compression Tests.
One Lead attaches to the Thick Copper "Red Cable" Post and the Other Lead connects to a Good Ground on the Solenoid. This
"Purple Wire Substitution" takes place whenever the Mechanic "Presses The Button" and the Starter Turns Over for as long as he holds that Button DOWN.
However, for the sake of Safety, the Mechanic should always ensure that any Vehicles with Manual Transmissions have the Shifters confirmed to be in the Out-Of-Gear NEUTRAL Position, with the Emergency Brake Set and the Drive Wheels either Chocked or Fully Elevated off of the ground on Pinned Jack Stands:
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