Hello I'm Neal and I am here to help resolve your issue. If I cannot help I will opt out and refer your question to another expert.
Is the starter clicking? Did it overheat?
starter doesn't click. haven't replaced starter, as car will start without problems on odd occasions.
not on hand today. what connections do you recommend testing
I want you start by probing for power at the small connector on the starter while you have someone try to start the car. If there is power when they try to start it then the problem in the starter. If there is no power then it is probably going to be the ignition switch.
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I need to retract the earlier statement about the starter. The engine will turn over but will not start. If one of the black spark plug cap it cracked and bulging could this have stopped the car from starting.
It could make it hard to start, especially if more than one is bad and wires are shoting out. I would fix that isssue to rule it out.