1977 20r toyota exh temp indicator light goes on\off???

According to an emissions schematic I have for 77 20R, the signal that energizes this warning light comes from the thermo sensor in the catalytic converter via the emissions computer. The schematic also indicates the converter temperature range of 1562 F thru 1688 F being relevant but I can't tell from this if the warning light illuminates in this range or if the converter heats up beyond this range (this would be my assumption).

What is also not clear is what malady is indicated and what course of action is required in both the short term and long run, when the exhaust temperature warning light illuminates.

If your 20R is in a 77 pickup it must be from California as anywhere else there is no catalytic converter in the 77 truck.

Hope this helps.

Dennis