“Leave a Light On” has an unexpected guest: George Harrison played the song's distinctive slide-guitar part. Belinda Carlisle suggested his name to producer Rick Nowels when they were looking for a guitarist with a unique sound, and Harrison quickly agreed to participate. He went on to contribute not only to “Leave a Light On” but also to another track on Carlisle's 1989 album Runaway Horses, “Deep Deep Ocean.” Harrison's contribution became one of the most memorable elements of the track and Carlisle later recalled that his widow, Olivia Harrison, told her that George had agreed to participate because he loved her voice. Harrison himself was also pleased with his work: he sent producer Rick Nowels a handwritten letter with instructions concerning the mixing of his guitar part, adding in a postscript that he had developed a blister while playing the song. For a former Beatle whose appearances on other artists' records had become relatively rare, his contribution made the track particularly special.