Any municipality in which, immediately prior to the effective date of this act, run-off elections were required to be held pursuant to the plan or form of government, or charter, of the municipality, shall, on and after the effective date of this act, be governed by the provisions of sections 14 and 15 of this act for so long as it continues to be governed by that plan or form of government, or that charter, except as provided in section 17 of this act.
N.J.S. § 40:45-20