The ECT button changes the shift points to be a little more agressive and will stay in that particular gear a bit higher in the RPM band for situations that you don't neccesarily want the tranny to downshift as early;it's helpful when towing.
Actually with the OD the light only comes on when the OD is off.
ok 2 conclusions, your bulb is burnt out, or its not working....
drive about 45-50 mph and hit the button, see if the RPMs change if so then its working and its a bad bulb, and if it dosnt change then that sucks! and i cant help you...