Look on the drivers side upper kick panel, under the dash. you'll either see a yellow, grey or green small square box with a small wire connector going into it. that is the O2 sensor timer.. There is a reset button in it that can be tripped with a bent out paper clip. I don't know how far your emission testing goes back but out here anything that old is exempt, so if it is the same there then just pull out the lamp, it is not a malfunction indicator light just a reminder lamp to have the O2 sensor checked and if bad replaced. HTH
Sorry bob that won't work with an 81 Toyota.
Looking for a Used Pickup in your area?
CarGurus has 109 nationwide Pickup listings and the tools to find you a great deal.
Search Toyota Pickup Questions
Toyota Pickup Experts