The factory water temp gauge has died on my 1993 GMC pickup (4.3L V-6 engine). I believe that the trouble has to be in one of three places, ie: the gauge, the wiring, or the sending unit that is mounted in the block between the cylinders on the drivers side. I suppose the problem could even be a combination of any of those. I need the step-by-step instructions to diagnose exactly where the point of failure is. Thank you.