Alfa Romeo Repair: 91 spider wont start when hot, dashboard lights, ground cable

Question
Recently, after driving for 15 miles or more my '91 spider won't start again for several hours.  Not a problem on shorter trips.  The dashboard lights and radio all turn on when I turn the ignition, but NO turnover.  Several hours later it's all back to normal.
I had tested a '91 spider with a similar problem 4 years ago when I was shopping for my car.  That car had been in the shop a few times to fix, but never any good solution.

Any thoughts?
Thanks

Answer
Sometimes it is the ignition switch. But, most of the time it is a poor ground between the engine block and the battery.
Clean the battery cable and post connections and take out the bolts attaching the ground cable to the engine and the body, clean and reattach--clean also the mating surface on the block and body.  Cold the ground is ok, but as things warm up the corroded fittings increase resistence.