The main/dip switch is a bit fragile and only has a relatively small contact area - especially the newer blue box replacements. I've had one of these burn out so I'd recommend using relays for a long and happy life (for the switch) - especially if using higher current halogens.

ok, i think a relay had been installed on the landy i got them off so ill have a look at it next time im up there....
did wonder why they had put them on a relay but that explains it all!!
my switch is original as far as i know and i did notice that the conctact pionts werent great, small domes....but i cleaned all the crap out of it and it goes alright atm...