I don't recommend a jury-rigged fix on an outdoor electrical cord. Wet grass conducts as well as anything else wet!!!
You can get a good 50-foot outdoor cord at any of the "big-box" stores. PLug it in & mow.
You "flake" the cord zig-zag at the starting place, and mow "away" from the starting point. Pardon if I'm sounding
pedantic.
Jim in Quincy MA
July 2006