I have a mk5 2003 1.4 Ghia Fiesta. I noted the front offside fog light wasn’t working so changed the bulb but still no joy? All other lights are working perfectly? Do the front fogs work off 2 different fuses/relays or is it a wiring issue? 

15 minutes ago, Bagpuss1_2 said:

... or is it a wiring issue? 

Wiring issue, or bulb holder. If you have, or get access to a multimeter, you can see whether a voltage is arriving at the bulb holder.

49 minutes ago, Bagpuss1_2 said:

Do the front fogs work off 2 different fuses/relays or is it a wiring issue? 

They are controlled by the GEM which is part of the passenger compartment fuse box

 

According to Haynes, no foglight specific relays in the cicuit, and one fuse for both front and rear fogs.....

Both lights and the dash indicator fed from a common point - does the dash lamp illuminate ?

Yes, the dash lamp illuminates 

The bulb you know is 100% working, take out and put in the non working socket. If it fails to light, you now you either have a broken wire, or, a rusty old bulb holder. You can try cleaning the holder up with a wire brush and a good dose of WD40. It's not a fuse (both lights wouldn't work), or the source of electric (from GEM) as again, both bulbs wouldn't work.