This is a description of how I tested my friend’s starter. After removing the starter, the command terminal was connected to the hot terminal from the battery. A positive (red) lead was then connected to the hot terminal / command terminal. A negative (black) lead was connected to the base metal of the starter. The starter was then clamped down. THE LAST STEP was to connect the jumper cables to a car battery. A good test result is when the starter both pops out (the function of the solenoid) and spins (the function of the starter motor). There is a good deal of attraction between the final connection of the batter terminal and the jumper cables. Do be careful if you choose to do a low-budget testing like this.
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