Won't start shortly after running for 20-30 minutes or so

[FeeAught]

True novice here. I'm having a problem with my 79 spider. It runs great, but every time I drive it for 20+ minutes or so, it won't start if I try to fire it up shortly after. I can jump it and it starts up without issue. The battery is essentially a brand new optima, and when I'm jumping it, it has plenty of juice. If it sits all day or all night, it starts up no problem. Well, it might click on the first few attempts at turning the ignition, but if it clicks, I know it will start eventually. When I don't get a click is when I know it will not start. It does not happen at all if the car had been at rest for an extended period of time (several hours+). Does anyone know what the issue might be? Let me know if you need any more info. Thanks in advance for the help!

[seabeelt]

Two thoughts. Check the connections at the starter and second check the connections at your ignition switch. Seems to be the two most common problem areas. You can also check the starter after running and it wont start by arcing a screwdriver across the two starter terminals. Be sure to make firm contact with the two studs and nothing else. ( Safety first - car is not in gear and the e-brake is engaged) Try these and let us know what you find.
r/

[Piccola]

It seems the tipical problem when the car gets hot and the temperature sensor gives wrong info.
In my '81 it is located in the front at the T coolant tubes.
There are 3 value that you have to check . Cold, average and hot and it gives different ohm resistance.
if you disconnect it , try to see if it starts.

[joeforum123]

I had the exact same issue, as described. I finally replaced the ignition switch and it has started perfectly every time since then! I too had the issue that it usually failed to start only after the car had been driven a while, then shut off, and then failed when trying to start again. Several turns of the key on and off until I heard a "click" usually meant is would then start.

Anyway, replacing the ignition switch cured the problem.