Over the weekend I installed Sea Level II tank monitor. I ran a new wire to all the tanks. The same two wire connects to all the tanks, and the senors are programmed by cutting tabs on the senors. The Gray and Black tanks are pretty easy to get to, but the Galley and Fresh water tanks are not so easy. I ended cutting a access flap to the Galley tank (it is right where the Left Rear brake wire are in case you are wondering), and a access flap just in front of the fresh water drain.
Since the temps were in the low 40's when I did all this, I had to stick a heater in there to warm the tank, before applying the senor (need to be above 60 degrees).
Sea Level Display on bottom
Here is what I ordered in case you were wondering:
http://www.bestconverter.com/709-4-S...l#.UTVBlaKPNod
Here is the wire I used:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1