You should be able to do it no problem.. Depends on how the SECS unit is wired up really.. If the water injection control is a switched-earth itself, then you should be able to hook it up straight to the dash.. if it's a switched-live, then you'll either have to use a relay (not nice) or a transistor (nicer, slightly more complicated).. i'm sure mr secs will make it all clear for you.