1. You just don’t have any horse sense when it comes to looking after yourself. You stay up late, don’t get enough sleep and eat poorly.
2. I took my father along when I went to shop for a new car. He has real horse sense and can spot a good deal.

The expression probably originates from the idea that a person who knew what to look for in a horse (i. e. , had a sense for horses) could find the best horses to buy.