I couldn't find a spoon, so I tried using a pen to stir my coffee. But that turned out to be a bad idea, because it got full of ink. The it is more likely to refer to my coffee than a pen because The coffee got full of ink.
In "I couldn't find a spoon, so I tried using a pen to stir my coffee. But that turned out to be a bad idea, because it got full of ink. ", The it is more likely to refer to my coffee than a pen because The coffee got full of ink.
This example is False.