electrical gremlin on lights

Hi Guys And Girls
I've got an s reg 156 2.0ts and its developed a problem with the lights only the o/s headlamp dipped beam comes on when switched on then if you flash onto main beam it wont switch off if you switch the lights off the headlamp stays on til you disconnect ther battery i have checked the bulbs they seem to be fine i have also taken the two earth leads from both inner wings and cleaned them up but to no avail

Any ideas cause i've run out

Cheers
Al

got this sorted had to call an autoelectrician he sorted it in about 20 mins