Hi, I thought that someone out there may be able to help me with information regarding repairs to the four wheel drive on my 2008 Ford F-150. The dash light goes on but the wheels don't go into gear. I recently bought a 'Chilton's' repair manual for Ford Pick Ups #26668, but it didn't have enough information in it. Particularly information regarding the vaccuum lines, actuator, or how to trouble shoot the system. If anyone knows of a publication which specializes in four wheel systems it would be appreciated. Thanks for any help you can offer.