Just went to get the truck smogged and on the way the sensor light came on and stayed on, Now I need to find out what the problem is, It's an 81 with a 22r motor is it an O2 sensor or what?

 

i have the same light on my truck.
apparently, it needs to be reset every 36k miles...or something like that.

look on the drivers side upper kick panel, under the dash. you'll either see a yellow or green or grey colored small square box with a small wire connector going into it. that is the "o2 ecu".

it has a reset button, but you can only reset it with something small, like a paperclip. once you reset it, drive it until the engine warms up and it should turn off.

 

in the likely even that the sensor is bad, replace the sensor and do the reset and once engine warms up, all should be good.


but since your truck is fairly old, i'm sure you could just remove the light buld that illuminates the "sensor" light and be done with it lol