In the schematic I have posted, there is a relays - yes - BUT it does NOT contain any wire colors nor does the relais itself contain any pin markings on it. No 240z wiring harness diagram shows the relais. Only that schematic.
So there´s no way guessing nor measuring what contact goes where.
Anyway, thanks for the good meant comments ?
Meanwhile I have received some pictures from a 73 owner of the corresponding plugs - maybe helpful for others struggling with the same problem.
I have learned, that the 28820-N3300 unit is responsible for the intermittent function of the wiper - it should even be possbile to wire the wiper motor and switch directly, loosing the intermittent function only.
From the pictures and my remaining wirning harness I will now figure out the correct wiring of the 3 components.