There are several steps required to test a starter solenoid, and none are very difficult to accomplish. You must first locate the solenoid to determine if it is in the engine compartment or underneath the vehicle; the solenoid is typically a small, black component with a large battery wire and two smaller wires attached to it. The voltage of the battery should always be tested before you attempt to test the starter solenoid, and this requires a voltmeter to do properly. Once satisfied the battery is not at fault, the positive cable on the solenoid must be crossed with the starter post to it. If the starter cranks, the solenoid is good; however, if the starter clicks, the solenoid requires replacement.
One of the first clues that a solenoid is on the way out is a slow, dragging starter or a series of clicks when the ignition key is turned. The difficulty in diagnosing a problematic solenoid is that a dead battery or a poor ground to the battery or solenoid can all give the same initial symptoms. When a faulty solenoid is suspected, the first step to test a starter solenoid is actually to test the battery. Using a voltage meter, the battery can be tested by placing the tester's electrodes onto the battery terminals. The voltage should read 12 volts. The next step, if the battery tested well, is to test the voltage at the solenoid.
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.
You can test a starter solenoid by manually jumping the solenoid as well. Using a long, metal screwdriver, you can test a starter solenoid by placing the screwdriver on the large bolt and battery cable on the front of the solenoid and the small terminal that the starter wire is attached to on the front of the solenoid. It is imperative that you make sure the vehicle is out of gear and blocked sufficiently before you test a starter solenoid in this manner. If the starter clicks when it is jumped in this manner, the solenoid is bad and should be replaced. If the starter cranks the engine over when the solenoid is jumped, you should shut the motor off and start checking the wiring and cleaning all connections.