Hi,
depends on actual problem but usually a fuse, if your quiet you can hear a relay click when you operate the switch. If so, inside the fuse box under bonnet, there is a small plastic panel lift it off and extra fuses there - don't think they are listed but worth checking those. The panel doesn't seem immediately obvious either - its like Vauxhall don't want you to find so look carefully. Also switches on them aren't very reliable either but obviously you won't hear it clicking then.
Lee
April 2009