Reversing light on my ford focus (51 plate) dose not work i have no voltage i have changed the reversing switch still not solved it can anyone tell me which is the live wire

You just go to the link I attached I'm sure you will get the solution of your problem -

https://www.reliable-store.com/products/1999-ford-focus-service-repair-manual

The G.E.M module isn't involved in turning on the license plate light's or the tail lights either ! Have you check the fuse's ? Do you know where the central junction box is ? F2.62 7.5 amp , F2.58 7.5 amp an F2.57 7.5 amp .
Parking, reversing and side lamps

• The voltage for these lamps is supplied through the lamp switch.
• The left and right-hand circuits are fused separately in the CJB.
• The lamps will work when the lamp switch is set to "side lamps" or "headlamps".
• Central Junction Box (CJB) (14A068) C270A
  behind dash panel, LH side

That should be on two different fuses, but everything goes thru the turn signal switch.
The switch might be faulty. A mechanic would check for voltage there.

Start by checking your fuses. Then put your ear against the wiper arm and have a friend turn it on. if you hear humming then the motor is bad and needs to be replaced. If all else fails check for voltage at the motor. there should be 3 wiree. One will have voltage all the time with the key on, one should be switched voltage and the last will be ground.

Hi does any ine no the code for my focus serial number M020244

If bulbs are definetly ok you can look behind trim on the left side in the boot, which covers the space between the boot floor and the window, you are looking for a green/red wire in a connector. this is the power cable which supplies both rear side mounted brake lights. You should check for voltage at this wire when pedal depressed. If no voltage you would need to trace this back to where the wire is joined in the loom as it feeds off the wire which supplies the high mounted brake light and you have stated that this works. Would still double check bulbs first though if you did'nt replace them. Hope this helps.

Its usually on top of the gear box and there is usually a black or grey plastic top you can take off.

speed sensor on the back of the gearbox failing

only one light not working indicates a bad circuit at the plug on the back of the light housing or in the wiring between the light and the dash swith