I should mention to clarify my posts that the diode inside the module only affects the operation of the power seats. The relay that provides power to the power seats can be thrown by either of two signals, the door being open or the key being in the ON position. The diode serves to keep those two signals electrically separate - so that they do not interfere with one another in other functions that they control.
When the diode is broken, the signal from the ignition key does not reach the relay - so the seats only work when the door is open. At least on my 87 300D that's how things were set up.
As for the power windows, as Steve mentioned they only work with the key in the ON position.