Hello Experts!

Here's one I don't know how to diagnose: wife's 2001 STS won't crank on occasion. Symptom is when she turns the ignition key there's 1 click, then nothing, no starter motor, no A/C fan. She wiggles and beats on the shift lever thinking it's a start/shift interlock issue, then finally it will start normally. This happens about every other month. Battery is fresh, no alternator issues, cable ends are clean.

So, what components need to be "happy" before turning the ignition key will energize the starter? Then, of course, how do I check them? I'm a "advanced amateur" mechanic and can follow a decision tree/check electrical continuity, etc.

Thanks in advance for your help.

TXsculptor