To fix starter solenoid problems, uplift the vehicle with a jack at a height that allows two jacks stand under the frame of each wheel. Raise the bonnet, and detach the negative terminal of the battery. Carefully remove the ignition wires and the main starter wire located at the back of the solenoid. Study the proper positions of the wire before reinstallation.
Using a socket extension for hard-to-reach bolts, untighten the large starter mounting bolts. Gently rotate and turn the starter to remove it from the mounting position until it moves out. Disconnect the starter from the solenoid post, and remove the backing plate from the solenoid using a screwdriver. Check the position of the balls and the springs on the plunger before plugging it out. Pull out the two studs on the solenoid casing and the old copper contact as well.
Fix the new copper contact, and reposition the stud. Secure the two stud bolts firmly but gently to avoid breakages. Fix the old spring and the ball on the new plunger, and push it in the solenoid until it fits perfectly. Confirm that the spring and the ball align with the plate seat, and then locate the solenoid plate on. Use a small socket to tighten the plate back on the solenoid.
Attach the thick wire to the solenoid, and then secure it firmly. Align the starter to the mounting surface, put the mounting bolts, and secure them firmly. Connect and tighten the main starter wire and the ignition. Remove the jack stands, and connect the negative terminal. Start the car a number of times to test the solenoid.