What is the green sensor that is under the alt. and is connected under the thermostat?

I broke it off and was wondering what sensor it was and if it would be safe to drive the car until I got a new one.

 

it's the water thermo sensor...when it's broke, the ECU puts you in "limp home" mode...totally sucks, been there, done that...about $45 at your local friendly Mazda dealer...If it's not quite "all the way" broken, you can try to push on the connector backshell & keep it there somehow to get it running...when it fails, though, you'll know it, it'll lose all power...

 

If the water thermo sensor fails/plug falls off.....the ECU defaults to a temp around 75 degrees. The car should still run. How good??? Depends. See your fsm for the real default temp that it fails to.