I think many Cadiz owners at sometime during their ownership of the van have had a problem with the Al-Ko ATC light taking its bat and ball home,we have certainly had one replaced a few months after purchase.
If out of warranty they aren't cheap at about £35 or so if my memory serves me correctly.
There may be various reasons why they go west but one may be water getting into the LED.
Came across this simple wheeze during the week,can't really remember where,but it involves simply gluing a plastic medicine pot ( like what comes with cough mixture or Gaviscon ) over the LED to keep the water out.
If it comes off or doesn't work then little is lost,worth a try.