I'm sure this is too late to help you, but in case someone else stumbles across this page (like I did) looking for information, I am providing the following and appending the website that I copied it from.--
The 'Fuel pump cut off switch' aka 'fuel inertia switch' is actually a reset button.
It is an extra safety feature which has been installed on Ford Motor vehicles for as long as I can remember.
It is not used (as far as i know) by other automobile manufacturers.
Since fuel pumps are usually INSIDE of the fuel tank, and fuel tanks are usually towards the rear of any vehicle , Ford has added this safety feature as a precaution.
In the event of moderate-to-severe REAR end impact, a fuel tank (or fuel lines) could rupture.
If the fuel pump continued to pump it could cause fuel to project through the rupture.
(I'm sure you can understand that this would be a 'bad' thing)
There are sensors in the rear of Ford vehicles (much like the sensors in the front of vehicles, that sense frontal impact & deploy airbags) that will sense rear impact & automatically shut off the fuel pump.
The switch is used to reset the fuel pump.
It works much like a circuit breaker in your home.
If you blow a circuit at home you go to the circuit-breaker box & flick the "red button" to the blown circuit to reset it.
Same concept here.
When the sensors shut off the fuel pump, you will need to reset/restart the fuel pump by pushing the reset button.
The reset buttons location is different for each vehicle (model) but on the Focus it located in the little recess in the kick panel in the passenger foot area.
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Often it is found in the driver's side area of the trunk.
As your body grows bigger, your mind grows flowered. It's great to learn, cause knowledge is power!
