I put the lights on whilst going through the Tyne Tunnel, the green warning light on the dash flickered and went out, there was a lot of vibration due to a very ridged road surface, I think the problem is within the switch stem, some thing has vibrated or broken off. After checking the fuses this will be my next thing to check. The Motorhome is a Knaus 708G on a Fiat Ducato 2.8JTD