It is likely that the key was turned on while the sensor was disconnected or that the cars wheels were turned while on a lift with the key on.
The fault will have to be removed with a scan tool (removing the battry cable might reset it but it will reset the whole car).
If it was a tire or wheel diameter difference or a sensor reading problem it wouldn't light the light till the car was driven.
BTW the 87 model would be entirely different. It wouldn't keep the light on unless the fault existed; unlike the self-diagnostics in the later car which keeps its memory.