Help ! My 97 f150 4x4 won't go into 4 wheel drive. The manual transfer case shifter is locking in the transfer case, but the vacuum valve on the differential shift lever isn't working. There is vacuum on one hose when 2 wheel drive is selected, but vacuum is on BOTH hoses when 4 wheel is selected thus preventing the lever from actually changing positions.Anyone know of a diagram or print on what operates the solenoids on the 2 vacuum valves ?