If the solenoid is under the vehicle, the vehicle should be jacked up and securely blocked. In order to test a starter solenoid, the positive test probe should be placed on the large bolt and wire attached to the front of the solenoid. The ground probe can be placed on the starter's body or the vehicle's engine block. With the probes in place, the starter can be engaged by an assistant. The voltage meter should read 12 volts for a good solenoid; any other reading indicates a problem with the wiring. [links]