I am hooking up aftermarket backup lights on my 09 F150 and will be using a relay. Pin 30 of the relay will be connected to the battery via a 30A fuse.
But I would like to connect the extra switch to a power source that is switched from inside the cab (fuse box).

From reading other threads people have spliced into existing wiring and I am not sure if this is safe to do so as more load is being put on the circuit.
Older vehicles use to have spare sockets in the fuse box to connect accessories but this vehicle does not seem to have any.
I do see on my truck too that the previous owner has spliced into a existing wire for something, this is how my fuse box area looks like.
So can someone tell me where would be a safe place to connect for power to my backup light switch.
Would it be ok to connect to any of these wires, if I recall correctly one of the yellow wires is switched.

 

If you are planning to use a relay then you know the draw on the line you tap into is minimal. Use an Add-A-Fuse or Tap-A-Fuse to connect to fuse #32 ... that's the delayed accessories for Sync, etc (at least on my year/model).

Or if you've already discovered the line the previous owner tapped into it ignition controlled then just check it with a meter and use it. The load will still come from the line to the battery when you use a relay.

 

Thanks Sharper, appreciate your input.