Starter Motor Troubleshooting Tips DIY - How to diagnose starter problems

Video to show how to trouble shoot a starter motor when it won't start the car. Provides a procedure to follow to diagnose starter motor problems.

One measurement I didn't have time to add was to verify the solenoid operation by measuring the voltage drop across it while triggered. When you turn the key to START and you get 12V on the trigger wire, put one volt meter probe on the big silver solenoid battery cable nut . Put the other volt meter probe on the lower black solenoid nut attached to the braided wire going to the motor. When triggered, you should see less than 0.1V between the two cable nuts on the solenoid. If you measure more than this then the solenoid electrical contacts inside are pitted or worn out and this is preventing enough current from flowing in the starter to make strong enough torque to turn the engine. Instead of turning the engine you will only hear a clicking noise when turning the key.

Battery Voltage - %Charged
12.6V 100%
12.4V 75%
12.2V 50%

Allowable Voltage Drop in the starter circuit
0.2V from battery +ve lug to starter solenoid silver nut.
0.1V from solenoid sliver nut to braided strap on starter body
0.2V from battery -ve lug to starter body metal.