They are closely related. However, honesty is a broader concept. Truthfulness means that you tell the truth when asked. Honesty means that you act fairly as well such as not stealing or cheating in an exam.If you cheated in an exam and told people, you would be truthful but not honest. Generally, people who do not act fairly lie in order to cover it up so a distinction is not necessary.
Honesty is adherence to right way of life viz. living on own labor, not cheating others any way. Truth is accepting facts and life as we see. However, honesty and truth are inter related. If you believe in truth, you are also honest. Lies and dishonesty are twin sisters.
Honesty is the way of life that is never to cheat any one where is truth what is actually the facts are. Even twisting them is like hiding the facts and making them look different from truth.