Hi,
It sounds like you have the same problem as i'm having.
if you take the plastic cover around the steering wheel off and look behind at the wires, there should be a blue wire for the lights, give it a tweek and it should turn the lights back on. thats the problem im having and how i deal with it, i find it keeps happening so will try soldering the wire on to see if it fixes it for good.
I am curious to see if others also have this problem and if so, how they dealt with it.
i have a 1997 def 90 and i also have a dim beam from the headlights as well as the sidelights when i put my sidelights on.
Hope this helps and makes sense.
all the best
Luke