i'm going to the boneyard tomorrow to pick up a thermostat housing for my s4 tii to tap for a temp gauge, so i searched around to find out if the s4 tii and n/a housings are interchangeable. then i checked mazdatrix's website and found that the s4 tii and 'auto' n/a housings are the same but the manual n/a's is different. does anyone know the difference between the two?

 

TII and auto NA thermostat housings have a threaded hole on top for the auxiliary e-fan temp switch, manual NA housings have that hole blanked off (no fan).