[SiriusHardware]

Pretty horrible choice of wire colouring (not yours, whoever came up with it).

From what you have so far it seems like the two blue wires are incoming AC mains into the filter, and the two black wires are mains outgoing from the filter. One black wire goes to terminal 2 of the mains transformer wiring and the other one should therefore go through the fuse, through the switch and then onwards to terminal 6 of the transformer.

Let's check this - take the mains plug apart and start at the neutral wire in the mains plug and measure for continuity from there to either the transformer terminal 2, or the wire going to the mains switch. Which of those two places does Neutral go to?

Same for the Live wire in the plug, check continuity, it should be connected either to the transformer terminal 2 or to the mains switch. Which is it? Your drawing shows it well enough, I just want to establish that the blue wires really are the input wires to the filter and the black wires really are the output wires from the filter.