The problem, most likely, lies in the voltage supplied by the adapter. For older iPods, the iPod Classic, and iPod Nano, Apple used a 30-pin adapter that charged over both the standard 5-volt USB signal or the 12-volt current that is standard in automobiles. However for the iPod Touch and iPhone, they switched to an exclusively 5-volt system, rendering many older car adapters obsolete if they use the 12-volt current for charging.

All is not lost, 12-volt to 5-volt adapters are available from many manufacturers, such as Scosche. Link below:

http://www.scosche.com/products/productID/1667