[werk_ag]

... Guess it made no difference switching the wires.

By the contrary it seems that it did a big difference. According to your graphics, during the last night, you got some spurious readings but this time they are no more than 3W/m2 most of them are only 1W/m2 (none of 12W/m2).
I think I already have explained why these readings could occur, also we don't know if the output of SP-110 is always at 0 during the night time.
Clipping the readings below 4W/m2 doesn't seem a big deal, it doesn't have any effect in the sunshine hours calculation (that only starts when readings are over 50 to 100 W/m2).

You can also try disconnect the ADC1 cable, currently there is nothing using it.