Front main light wont work when new blub fitted v reg fiesta

First ensure that power is getting to the bulb connection behind the headlight. You can use a 12v test light to do this or use a known good bulb. If no power to the bulb connector, check the fuse panel on the lower left of the dash and look for the fuse for the headlight lamps and replace if necessary.

First put the new bulb in other side and test just incase of faulty bulb, Then you need to start cheaching if any power is going down to conector with test lamp.