I would take Mark's input anyday over others
He has years of experience wiring vehicles and will only sell you a system/part if he knows it will work for you - and he is there to back up his stuff if needed.
As mentioned above, wire has a given resistance per foot depending on size.
The smaller the wire size the more resistance it has and the more it restricts the final voltage available to the device (your pump in this case).
14AWG wire has @2.5ohm's-per-ft
10AWG wire has @.8ohm's-per-ft
So, if you do the math
You are feeding the pump (guessing it's @20 amp load max, many are around there) with 12vdc and the length of the feed is @12ft, then the final voltage available at the pump would be less than 10vdc if you use 14AWG wire - however it would be @11vdc if you use 10AWG...
so a 14 gives you a 2.5% voltage loss vs 10 which gives you less than 5% loss - I think you can see why going to a slightly larger wire pays off quite often.
I'm pretty sure Mark already fiqured this out for you.
Fear and common sense should tell you a Fuel Cut-off system is the only way to go
If there is no oil pressure closing the contacts on the pressure switch he sold you, there can be no power to the system and fuel can't be continually being pumped to your non-running engine.
In an accident or roll-over with just an On/Off switch there is no way to be assured that you, or someone, will be able to turn off the switch so fuel will still be being pumped - maybe into a area you don't want it be
All modern cars have a pressure interlock switch or an inertia switch that cuts power to the relay if the car is in an accident or rollover - it's part of the ECM/PCM.