Well I have done it, I have the Alpine N099 unit, ran it from the speedo in the end, on the red speedo stalk on use the far right hand purple cable. Feed into that, for some reason I couldnt get the ISO purple cable to work with it, even after testing. So try that, works a treat. To be honest im not too sure what Eddie is talking about as its totally legal.
Posted this a few times mate, dunno if you have some knowledge bank on the site somewhere as this would be useful to go on.