How can I fix non-functioning dip head lights on my 54 reg 1.7 D combo van?

Can anyone please advise on a possible fix for the non-functioning of dip headlights on a vauxhall 54 reg 1.7 D maxx combo van. I switched on lights and within seconds dip headlights went off. Side lights and main beam still operate as normal but both dip have failed. Both bulbs and fuses have been checked and found ok. Two weeks before I had cam belt changed so checked engine bay for any connectors in same area as work would have been carried out as I thought a plug could have been dis-lodged. But I could find nothing. A friend said that the light stalk on the steering column may be faulty, so I changed that with one from a scrap yard, still no joy. Has anyone got any ideas where I should be looking please.. thank you.