This basic piece of start systems is not as mysterious as it has been presented. Four wires and that's it.
There are two physical configurations but they are functionally the same. The second, later, version is actually the sturdier of the two.
This is the old standby. This bracket mounted 12 volt version has been around since the late-50's. And there are two bracket configurations. One flat, one angled. Other than that, they are the same.
In the mid-80's the unit was upgraded to this is flat mounted base. It is supposed to be the bigger and badder version of the solenoid.
This graphic is really as simple as it gets. Three, possibly four, wires and it gets the job done. The I wire hookup is used only vehicles that used a ballast resistor. Not all applications use that wire but most aftermarket replacement units have it.