3.6 stops dead for 15 minutes, then resumes running . . .

[Flakbau]

My 3.6 liter supercharged 1982 911 - based 935 tribute developed an unusual problem over the last summer. It typically ran fine, but occasionally would lose complete ignition for 15 minutes, then start again and run fine again. There was no discernable pattern, except that stoppages typically occurred only when the engine had achieved normal operating temp.
I hunted around for advice. The two best tips were faulty ground and the crank position sensor. Recently, I took the car in for repair and handed the tech my two tips. He went straight for the crank position sensor. Mine was producing only about half the resistance required. He replaced it and all is well. He agreed with my tipster: when a faulty sensor heats up, if often goes offline, and the engine will crank but never once any ignition. A good tip for anyone else who experiences this strange problem!