With GM Delco starter motor mounted solenoids in INBOARD #8 stud marked "S" is the one that activates the starter motor. OK what happens when the ignition switch is twisted to the start position?
Power is sent to the S terminal.
An electromagnet inside the solenoid pulls a piston which engages the starter gear to the engine flex plate teeth
At the same pull a copper disc is yanked forward until it smacks across two coller bolt heads inside the solenoid.
Is the solenoid magnetic coil grounded?
Of course.
But it is grounded by a circuitous path through the armature and field coil windings.
The solenoid demands 14 amps. This is an awful lot of power to force through an agnition switch. And power to the solenoid MUST pass through the NEUTRAL SAFETY SWITCH located on the steering column under the dash.
Parts Stores rebuilt 10MT starters are utter garbage. If a Delco try and get a genuine Delco remanufactured starter. Same with a Ford starter. The reclaimed garbage most mass rebuilders use would gag a maggot.
Finally if your rig has a metal case booster relay JUNK IT. Use a black plastic case genuine Ford style starter relay. You must add a ground wire from the cad plated steel mounting bracket to a good grounding point. Also I have seen pricey gear reduction 10MT replacements. They spin the engine faster using 1/3rd the amperage.
Hope this helps