Intermittent ignition help

'69 Barracuda convertible, 318, auto trans, Pertronix ignition module. Have intermittent problem where car won't start. Have lights, horn, etc, but no click or starter engagement. Shifting trans, repeating turning key, tightened positive battery cable has no effect. If left for a few days or weeks, will start up and run fine, until happens again. Replaced neutral safety switch and connector, but no change. No discernible pattern to issue, other than has always happened in the garage(fortunately).

Any guidance to what to check?

Thanks!

Mark