Hola Alan-my memory's not what it was but I seem to remember a recall for these, I did some for the main dealer.
It was a loom/relay mod...water gets in to the relays under bonnet.
i think the main culprit was dim dip, but it affected sidelights too?? worth a look anyway.
If u still want a wiring diag, i've got the book here somewhere-probably under my bed! ))
hth ian(n)