I usally hard wire a radar detector into the fuse block, so that it comes on when ever the truck is running. How ever in the 2004 f-150 there does't seem to be an "ignition type" power source. It seems every thing is always powered at the fuse block, and is powered on or off somewhere else.
Any Ideas?

 

Main ignition harness going up column to ign switch. Dark Blue with green stripe = main switched feed.

Strip off ~1/4" of insulation, wrap radar det. feed wire around ign wire three or four times, solder, insulate connection (GOOD electrical tape, like 3M Super 33+, with a zip tie holding the tape incase it decides to unwrap), install 5A fuse inline as close to tap as you can...

 

Works great!