RGB SCART cable kit
Harlequin RGB + stereo audio to SCART cable
This cable passes through RGB video and (mono) sound on Harlequin 128K models, e.g. Harlequin rev 2D, ZX Nuvo, etc.
It has stereo audio, which plugs into the right mini-jack socket (seen from the front of the machine), closest to the edge connector.
With the ZX Nuvo, make sure that pin 8 of the RGB socket is configured to Composite Sync, by setting the jumper on J9 to position 1-2.