Had another look at the wiring diagram once I'd sorted through the fusebox labelling errors! Although I earlier suggested otherwise, there is a 15 amp fuse 10 in the main fuse box that should be labelled "Indicators and headlamp flash". This feeds the light switch on the afore mentioned green wire when ignition is on.
If this fuse is found blown, it would explain your problem Carl, although sidelights wired outside ignition circuit should work normally. If it blows again on replacement then very likely the light switch is faulty as previously suggested.
