As expected, going home it did not hold the set speed.
The switch did work as an extra accelerator pedal. Obviously the switch works fine. Tomorrow morning I will try to confirm my theory of breaking down when warm only.
My question is this: Will driving around with the cruise control amplifier removed cause any harm?
I will order as many components as I can get and replace them.
Will update when done, most likely will create a new thread with the findings.
If anyone reads this before I attempt to fix it, and knows which components go bad in the cruise control amplifier circuit board, please post it.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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