Ron - Wilbur was inquiring about the battery NEG cable. Wilbur, its sandwiched between the upper right rear motor mount, and frame and motor.
Skip the continuity test, Ron, switch straight to ohms. The strength of the resistance is what is at issue, not if there is continuity. Check the resistance between battery NEG terminal, and the bolt on the starter, and/or to the starter motor housing.
Also, lets be REALLY obvious. Battery voltage please? Your description of the solenoid behavior indicates a solenoid contact issue to me, not a ground issue. You can open it up and clean the contacts, or swap solenoids. Lastly, is the ground wire for your solenoid solid? (Meaning, correct and tight and clean?) One is power, the other the ground. Try using some jumper wires for it to force it to operate the starter motor.