Fiesta strange foglight query

[macp]

Got a call from swmbo telling me her rear foglight had come on and was stuck on even if she turned off ignition and removed the key etc.I drove out to her to see if I could help worried it would drain the battery.Sure enough the foglight was stuck on and would not switch off.I was going to remove the switch and clean the contacts etc but it looks like you have to get in behind to remove it so I have made a temp fix by removing the fuse.

Could it be the switch or the relay do you think ?

Car is a 2002 Mk4 Fiesta.

Thanks in advance.