They are *mostly* independent and will work fine with no connectivity, but you can get some additional control of them via the ECU if you chose to do so. Factory inputs to the SW20 EHPS controller (that matter) are vehicle speed, and PSCT (PS cutout signal), as well as a PS pressure feedback switch that functions like an idle up request. The PSCT signal you can use to cut steering assist fully in certain situations (defaults to on, so obviously you can leave it disconnected if you dont care), and the speed signal you could modify if you wanted - the factory wiring on both the mechanical and electric speedo models runs the speed out from the gearbox straight to the dash, then a separate "speed output" from the dash goes out to EHPS, cruise control, etc. This is still a square wave output so if you wanted to "lie" to the EHPS unit about your speed, or you have changed the wheel size/gearbox sensor/swapped to an aftermarket dash, you could change this wiring so the gearbox feeds the ECU, and the ECU feeds a corrected signal to the EHPS unit + other control units directly.