A motor vehicle dealer licensed to sell motor vehicles may operate one (1) additional business at the dealer's established place of business; provided, at least sixty-six percent (66%) of the dealer's established place of business is used for the sale or service, or both, of motor vehicles and that the income derived from the additional business is less than thirty-three percent (33%) of the gross income of the dealership. The dealer may also install signs at the dealer's established place of business for the purpose of advertising the other businesses.