Why would the engine light come one if you put ethanol gas in a non car?

The engine light wouldn't come on if you put ethanol gas in a *non-car*. The engine light is a feature of vehicles with internal combustion engines. A non-car, like a lawnmower, chainsaw, or generator, wouldn't have an engine light.

If you put ethanol gas in a vehicle *not designed to handle it*, the engine might run poorly, stall, or suffer damage, but the problem wouldn't be signaled by an "engine light" because that's not how those machines operate. The consequences would manifest in different ways depending on the machine.