What year truck are we talking about?

The 2.3/2.6 motors (at least in the 89-94 Amigos) have an eccentric gear that turns the light on and off. It rotates once every 90,000 miles.

You need to move a screw from one hole to another to shut the light off. Here are some pages from the manual to shot the process. I think my page numbers are mixed up.

O2 Sensor