I believe you are talking about what, in my manual, is called the reserve fuel sensor. It is on the underside of the tank, under about where the backmost part of you dash bezel is. There is a metal plate there with 4 nuts (!!!!) and a 3-wire harness on it. In my manual there is a pic of it on page 19-25 where it tells how to test it. I have not removed it so do not know what is involved but I believe this is what you are asking about. I believe your my 2007 1800R S2 is set up the same as yours in this regard. Hope this helps at least with location.