Accessory Wire Under Hood 2004 Expedition

I have a 2004 Ford Expedition and need to install a self made X-10 Car Sensor under the hood.  I need to know where I can tap an accessory voltage source (+12 volt when the vehicle is running, no voltage when the vehicle is turned off).  I searched for this information and noted it contained wiring harness information color code, but I'm not sure where this harness is (or if is is) under the hood.  Any location under the hood will do as I plan on installing this unit behind the front grill. 

Thanks in advance as this information will greatly help me!

I added some pictures taken under the hood of the 2004 Ford Expedition to show possible wiring harness locations:

Here is the general area under the hood.  I circled one possible harness location to use:

Below is a closeup shot of that wire harness location:

Below is the "left side" of the engine where possible wiring harness locations exist for the accessory source.  There is a two wire plug that is just sitting in a dummy receptacle (not doing anything) on the far left, but no voltage existed on any of those pins to ground when vehicle was running (anyone know what that does)?

Below is a closeup of that two wire terminal:

Hopefully one of these harnesses can provide a 12 volt accessory source.  I will also place an in-line fuse where ever I tap off!  Thanks again for any help.