wire knock sensor negative to sensors ground

* yes: EC36/pin26 is sensor GND, good for knock-.

* note: EC18/17 is NOT GND when ECU has 2nd WBO2 heater FET

** either for dual-WBO2, or for other use (very practical). So using EC18/17 needs verification (connectivity to EC36/26), and need extreme care when plugging in another ECU (which might have EC18/pin17=2nd WBO2 heater FET instead of GND)

----

If ECU is ordered with 2nd RS232, then ECU is equipped with 2nd RS232 TX and RX, see the EC10 paper included with the ECU.

Otherwise the 2nd RS232 may or may not be available on EC10, but 2nd RS232 is always available internally,

* on 3 pin header (RX,TX,GND)

** between ST232 / MAX232 chip (near pin8,9) and main processor,

* note: The pinout is similar to the 1st RS232 SV2 header GenBoard/Manual/CommHardware

* also see : GenBoard/VerThree/Schematic