WASHINGTON — Ford Motor Co., General Motors Co., Stellantis NV and Toyota Motor Corp. sent a letter to congressional leaders Monday urging them to lift the 200,000 customer cap for existing electric vehicle tax credits. The letter from the nation’s four largest automakers comes as Democrats in Congress are negotiating with Sen. Joe Manchin, D-West Virginia, on the shape of a potential climate and energy package that originally included a controversial EV tax credit Manchin has called “ludicrous.” Car buyers can currently qualify for up to $7,500 off the cost of a new electric vehicle — but onl…