Thanks for the reply. I've checked the earths behind the dash around that area and they seem ok. Everything else works perfectly on the car except for the dipped beams and mains. With the ignition off just the sidelights come on as they should but with the ignition on the dipped beams come on but not as they should.

If I was to put a meter on the back of the main/dipped bulb what voltage should I see on what colour wire with the switch in what state? There are 3 wires going to each bulb, white, yellow and brown.

Thanks