There are a few different modes that you can put the ECU into for diagnostics, and thats one of them ( although I think it only works on the ZX and SX ecu's ). IIRC the light comes on above 14.7:1 and goes off below, its for checking that the lambda sensor is working in closed loop mode ( the light should flash on and off )
If I remember later I'll post the various modes and how to access them, although the Pulsar ecu is very limited compared to the other ecus ( which have a mode selector switch on them )