Check Engine Light comes on when car fully warms up....

the wiring on this pickup seems a little weird
the car is a 1991 chevrolet s10 pickup, 2wd,4.3l automatic.
The car runs and drives fine without a problem but when the car is at its normal operating temperature a little below half 210 degree it throws the check engine light, and it stays on, it only happens when its at normal temperature,
i was thinking the wiring was wired up wrong can that be it? if so what should i look for?
what turns on when the car is at normal operating temperature?
The fan? can it be grounded at the thermostat?
It only a distraction to me worst come to worst i;ll tape it off lol and dont see it.
but i would like to solve the problem first. thanks

It does not overheat either.

heated oxygen sensor is my guess.

should i just change it?

dont guess get the fucking code read its a obd 1 u can buy the 10 dollar code reader. dont throw parts at something u will end up spending a fortune on nothing

advance auto can read your obd1 system bring it down to abbott and ridge