A bill that would grant significant benefits to the dealers at the expense of manufacturers is headed for a state Senate vote, four years after legislation that also favored dealerships in their relationship with carmakers won approval. The bill, which appears to have significant support, is one of 20 dealer-initiated bills in 14 states covering similar ground, according to the Alliance of Automobile Manufacturers, a Washington, D.C.-based lobbying group for carmakers, which says the legislative activity is typical in the year-in, year-out battle for power between the dealers and manufacturers.