There has been a failure of the door locks on the 740 wagon the Tale gate unlocks with the drivers door and no other function works the Chilton book is of verey little help, no wiring diagram for a 90 740 or other door locks . Do I need a new Lock actuator or is there someting else to check??

There is a switch in the driver's door that sends a signal to a relay mounted on the central relay panel. The relay then sends power to all the lock motors (all doors except driver's door). If some of the locks are operating and others are not, then you have either a wiring problem or a ground connection problem. Either eay, the place to start is to remove the door panels on those doors that are not working. Unplug the lock motors and check to make sure they operate freely. If so, proceed to check the wiring with a multimeter - look for bad ground connections, no power on lock/unlock leads when door switch operated, etc. I expect that the three passenger doors are on one harness and that the tailgate haas a separate harness lead that comes from the relay. So look for those points which are common to the three passenger doors.