thanks for the response, thought it might be different for the stagea.
i just got a response from matt at nistune, ecu boost sensor is pin 47 ( at least on the r34 ), had a look on my S1 C34 stagea ecu loom pinout and there is no wire so confirmed s1 stagea didnt come with boost sensor ( s1 c34 runs s2 r33 engine with r34 type ecu harness).
does anyone with a c34 know what that plug is for?
i will most likely unpin it from ecu harness and pin it into pin47 for boost sensor on my neo nistune setup for s1 stagea