if you ever took apart an instrument cluster (DONT ASK.......) there is a separate odometer counter above the actual odo. At 90,000 miles the dial (number wheel) at the end has a step in it (see pic, its smaller), this actuates a micro switch in the back (see pic) and throws the light on....then after 90k more it shuts it off. Now replacing the screw from one point to another reverses the switchs polarity and shuts the light back off until 180k when the switch activates the O2 light again. The pisser part is, its mechanical, so if you lived with it, like Tad, from 90,000.1 to 179,999.0 and you reverse the screws at 179,999, it will go back on at 180,000.... it doesnt know where the screws are and that you just changed them.....Tad said:I've always wanted to know if the 02 light that comes on at 90k miles would go off at 180k miles, if it were left alone. Yesterday I proved that it does! on at 179,999, off at 180,001. So, unless the light bothers you, just wait another 90k miles and it will turn off on its own.