In this day of high-powered and intrusive automobile electronics, it is hard to get people to believe the explanation of the lambda light. The light itself is an indication in the top right of the instrument cluster that shows the word "LAMBDA" when lit.
It is not a "check engine" or "MIL" light as we know it today. It is wired only to a percentage counter PN 101606 that causes the light to come on when the counter reaches 100% at 30,000 miles per the odometer. The light will stay on until the counter is reset or the counter unplugged. After being reset, this interval counter will count another 30K miles, from the point of reset, to turn the light on again. Notice that the the function of the light is not to monitor the operation of the engine or its emissions control system, but merely to remind the owner that the factory recommends that the engine be serviced. To reset the counter, you must turn the small button on the side of counter until the dial registers zero. It is usually necessary to remove the counter to do this. It is located on a bracket that straddles the steering column near the driver's feet. On early production cars, this bracket usually also carries the inertia switch, though on later cars the inertia switch was repositioned to a spot near the luggage compartment release handle. Both the upper and lower speedometer cables terminate into the counter.
Revised 1/13/2022 ET (formatting and links)