Leif,

I studied the wiring diagram in the Haynes manual, and I could not see what
could be failing in your Van. The power for the light switch comes from two
sources. 1st source is straight from the battery (marked 30) and powers your
parking lights (58L & 58R) and instrument lights (58b). The 2nd source is from
the ignition switch (marked X) and powers the head lights (56). Now, we'll
concentrate on the 56 circuit. It runs from the head light switch to the dip
switch / turn signal lever. The dip switches the 56 (input) into 56a (high beam)
and 56b (low beam). The light horn gets its input from 30 (battery), so it is
separate from the light switch. From here, the 56a and 56b runs to the fuse box,
where each lead is split in two, with one fuse for each light up front. From the
fuse box, it is straight forward to the lights.

What you need to do is check that you get power from X to the light switch, if
yes, check that 56 is positive with the switch "on". If yes, you must move on to
the dip switch. Check that both 56, 56a and 56b are all positive. From there, it
goes on to the fuses, and to the lights.

Now you have the path of current, so you know in what manner you must search for
non working parts. Replace where necessary!

Good luck,

PerL