U.S. upgrades probe of Mercedes car rear-light issue DETROIT (Reuters) - U.S. safety regulators upgraded an investigation into more than 250,000 Mercedes-Benz C-Class cars for possible failure of the rear lights. The U.S. National Highway Traffic Safety Administration upgraded its probe to an engineering analysis of 252,867 C-Class cars, from model years 2008 through 2011, because the rear lighting could fail due to an overheated electrical connector, according to documents filed online. An engineering analysis is a step that could result in a recall of the vehicles by the regulator. In some cases, the overheated connector resulted in melting, smoke or fire. Regulators and Mercedes, a unit of Germany's Daimler AG, have received 402 complaints about the issue, including five incidents alleging fire, and one injury, according to the NHTSA documents. A Mercedes spokesman said the company was cooperating with NHTSA's investigation. A preliminary evaluation of the problem was initially opened in July after NHTSA received 21 reports of rear light assembly failure due to the melted electrical connector or housing. Mercedes said the overheating of the ground wire was caused by corrosion between the connectors in the ground circuit to the tail light, according to the documents. Analysis of the complaint data indicated an increased likelihood of failure as the vehicles age, so the investigation was upgraded to further study the risks and frequency of the issue, according to the NHTSA documents. Reporting by Ben Klayman in Detroit; Editing by Bernadette Baum