Connections are labeled on the PCB.
Make sure the sockets used do not allow electrical contact between RCA Socket ground and the chassis. Connect each RCA input pairs ground connection to the middle connection of a given input connector. Connect the signal wires (L/R) to the respective connections of the input connector.
Up to five inputs can be accommodated.
For single input applications this input can be connected to REC OUT (ie tape out) connector, bypassing the input switching.