do this test, take the cable DB15 - CARB and measure with an ohmmeter between pin 7 of the socket on the CARB (which corresponds to the K-line) and pin 7 of the DB15, then take the cable DB15 - BOOT and you will see that the green area corresponds to the K-line...in addition to the 12V...it's just that, I suppose, one of the relais exchanges the K-line and 12V depending on the driver used by configuring cos? the green according to customer's need?...here, one determines a way of working that is unique.