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Thanks for the added info.........
The only way to check is when it does the "no crank"..You need to check voltage at the Solenoid while the key is held in Crank position.
On a 1970, there isn't any snesors, other than the Park / Neutral Safety switch, but that will be confirmed when you check for voltage on the Starter wire
If there is voltage from the Starter wire to the Solenoid & there is voltage at the Battery Cable on the Solenoid, then you would try to jumper across the Solenoid to see if it will crank. If not, then the Solenoid is still the culprit & needs to be changed to a better quality Solenoid.If no voltage present a the Starter wire, then you will need to back probe it until you find the source.Usually the Park / Neutral switch or the ignition switch.
This needs to be done only when you get the No Crank, otherwise you will just be replacing parts