MARLBOROUGH — Developers of a proposed 140-unit apartment complex at the former McGee Farm property on Boston Post Road East (Rte. 20) pledged $200,000 to study, design and construct a traffic light at the entrance of the facility. But members of the City Council’s Urban Affairs Committee continued to stress they cannot support the project without a guarantee from the state that a traffic light will be installed. Waypoint Residential, a Stamford, Connecticut-based development company, is seeking a special permit to build a three-building apartment complex at the site. The company initially planned to build a 188-unit, four-building development, but scaled back its proposal in response to concerns from neighbors and city leaders.