I have an 08 head unit I am going to install in my 04 (New Body style) F 150. I hear that I may need an antenna converter for my 04 antenna going into my 08 head unit. If this is true does anyone know the part number? Also does anyone know how difficult it is to use the 12v lighter plug in my dash as a power supply for the sirius unit that came with the 08 unit?

 

I used this in my '07. I'm sure yours would be similar:

Metra 40-CR10 Chrysler Vehicle Antenna Adapter Cable

I found it at Best Buy for pretty cheap.

As for using the 12V plug to power the Sirius tuner I did that and it works fine. I simply used some wire taps on the wires to the plug behind the dash and made sure to use shrink tubing around the connections to insulate them well. Works fine since the Sirius tuner uses very little power and the 12V plug in the truck is also fused. I soldered my connections but you could simply use butt connectors if you wanted to.

 

That factory Sirius tuner is jumped off of the radio power plug. I would just try to use that power source. I believe you can even get a harness converter to add the OEM sirius tuner.

 

I actually powered my Sirius bus controller and my PAC steering wheel controller from the 12v cigarette lighter in the dash. The wires are clearly marked (black is ground) and easily accessable. Just use some radio shack wire taps and it's simple. I have some pics in the Avic-D3 review I did that may/may not help you.