the bulb failure module is down behind one of the a pillar kick panels, but it won't be that. what you have, particularly on the rear lights, is a typical ford bad earth.

the rear disco lights are very common to old fords, you just need to clean up the earth connection on the light board, and i think there's one that bolts onto the rear panel inside the boot (near where the jack bolts up).

is the problem with the dipped beam that it dooesn't work on the passenger side? i believe that the passenger side headlamp takes it's earth from the drivers side one. check tah tconnection.