Trade your Xterra for a manual tranny one and don't worry about temps
The 6 speed manual is wonderful.
On a serious note, try the Xterra forum (ThenewX). Chances are, someone has done what you are trying to do.
I spend my last Saturday changing all fluids on mine (manual tranny) and all my fill and drain plugs were covered in mud. Not sure I would want any wires in there - they will not live long enough.