The starter disc inside connecting the main terminal to the armature may be worn. Kits are available to replace them. Do a voltage drop test. Positive battery to positive post of the starter. then try to crank. Volt meter should read less than 1 volt. Also test the ground side negative battery post to starter case. should b the same result. If so pull the starter apart and check the disc.
https://www.amazon.com/Starter-Solenoid-Starters-Chrysler-Plymouth-x/dp/B008U80X5G

Doug