If this is a modern car with the integrated starter solenoid on the
side of the starter, it will have three posts minimum.

 (The old Autolite system had the power switching relay up on the
fender, and the solenoid used to swing the Bendix drive gear out was
simply a movable pole piece on the side of the starter motor.  The
pole piece cover is shaped like a wedge, with the fat end away from
the flywheel.)

 The big post with the big wire is coming in from the battery.  

 There will be a small post (#8-32 or #10-32) with the wire coming in
from the ignition switch "Start" circuit - that only has 12V when the
key is turned.  (Some new cars have a quick connect on this wire.)

 If you put a "Remote Start Switch" (a simple normally-open push
button switch and two clip leads) between the battery lug and this
small solenoid windings lug, the starter motor will run when you push
the button.  This indicates an open in the start circuit - the most
likely one is the Neutral safety switch or an alarm system.  Try
starting in Neutral instead of Park, and in the other gears with your
foot on the brakes.

 (If the engine RPM flares on start like normal but you're starting
it in gear, the car can try to move even with your foot hard on the
brakes - do this somewhere you have room in front of and behind the
car, in case it does.)

 There will be a heavy post with an odd crimp lug going down into the
starter through a grommet - that's the switched power from the
solenoid contacts to the starter motor windings and brushes.  Don't
mess with that one, unless you want to make lots of pretty sparks and
melt big chunks out of the side of your screwdriver.

 On older cars there's a fourth wire that feeds switched 12V from the
starter back to the ignition system, and overrides the coil ballast
resistor to get a hotter spark during starting - they literally use a
6V coil with an inline ballast resistance.  You won't see this with
electronic ignition.

   --<< Bruce >>--