well i got a new motor in and running and now the add coolant light stays on all the time the temp is fine and the system is full anyone know wat it might be or had this problem b4

 

bad sensor

 

I also had the same problem after a partial topside rebuild. Im now rebuilding the whole engine and havent put it back together. I believe the sensor completes a circuit when in contact with water, so you should be able to use a VOM to see if the sensor is shorted. If its okay then your probably looking at a break in the wire somewhere. This is what I believe is the problem with mine. As such, Im rewrapping (rebuilding) all the engine compartment wire harnesses. The shields, covering and tape are very briitle and "crunchy" when moved.
chiuck.

 

I had the exact same problem b4 after reinstalling the engine. Make sure you connected the one wire going to the AC compressor( ground for the clutch ) to its right connector because... in the same area..(behind ac compressor), theres another connector close to it enough to reach it and you might accidently connected to it, they both have the same style connector and will fit both, make sure they're the same color(black to black and white to white). I went what your going through, your coolant level sensor is fine. Your pretty much grounding you level sensor from the AC compressor clutch activator. Reply back if it worked.

 

check the wire too...

 

Check the sensor, wiring and then just run it for a few miles and then unhook the battery overnight to reset everything. This is what worked for me when i had the same problem.

 

I had the same problem. I bought a new sensor to no avail. Ended up getting a "new" gauge cluster from a mazda salvage yard and it fixed the problem.