DETROIT (Reuters) - U.S. used vehicle prices have shown signs of stability the past three months, likely relieving some of the pressure on new truck sales and the prices consumers will pay for them, analysts said. That stability potentially could provide support for Ford Motor Co(F.N: Quote, , Research, ) and Chrysler LLC's key new pickup truck launches this fall, analysts from Barclays Capital and JP Morgan said in notes to clients. Used-car prices are a closely watched barometer for new vehicle sales as a majority of purchases involve buyers trading in an older vehicle and better prices tend to spur more trade-ins. The Manheim Index, which is based on used car auto auction data, rose 0.1 percent to 110.8 in September from August, but was down 4.3 percent from September 2007, according to analysts. Barclays analyst Brian Johnson said that pricing for large SUVs and pickups also continued to show sequential improvements in September That 'is particularly positive for Ford as it launches its F-150 full-size pickup over the next few months,' he said. Sales of new large trucks and SUVs plunged in May and June as consumer demand shifted toward smaller more fuel efficient vehicles amid a surge in gasoline prices. The record gasoline prices also battered resale values of most vehicles, with the decline most pronounced in the truck and SUV segment. Used prices plunged, especially, for big trucks such as the Ford F-150, Chevy Silverado and Toyota Tundra and forced lenders -- including finance companies like GMAC and Ford Motor Credit -- to write down the value of vehicle leases.