Reading the codes could be a solution...
I didn't answer Settra's earlier issue with reading resistances - ie, "... the resistive sensors are a problem for many reasons. mainly because, since their resistance changes, you cant use a diode to isolate the grounds...". Hence the desire for the common grounding of sensors and the avoidance of non-linear insertions - eg. diodes.
But the sensor's voltage can be compared to a map or maybe calculated to derive an appropriate output eg, 0.6V = 0; max 7V via 18/25 voltage divider as about 3.0V = 100%; 3.9V => 55%, etc. That's the beauty of using uPCs like Arduinos, PICs, etc - the input signal mapping is programmable.
As long as the measuring doesn't effect the line's voltage or current (ie, as high Ohmage/impedance as possible) things should be fine. (If not, use a voltage follower or buffer.)
Isolating thru diodes should generally not be necessary.