Also carefully check the wires going to the starter. All of them. Just around the beginning of this year, I had all sorts of weird stuff going on with my starter (1980 242). Sometimes wouldn't start. Sometimes wouldn't turn off. Turned out to be a bunch of wires under the hood had deteriorated from age and heat. The insulation on at least 6 different wires was compromised to the point that wires were rubbing together and shorting out on each other. I replaced all affected wires and the starter is working just fine now. I found the wiring problem after looking at everything else first... starter, solenoid, ignition switch, etc. Never suspected the wiring under the hood. What made this difficult to find was that the wires that were damaged were all inside of a sheath concealing the true condition of them.

billy242