One of the biggest complaints about the 2005 Mustang is the relatively huge antenna and base that is on these cars. My solution was to delete it completely without sacrificing AM/FM reception.
I used the Metra UA-205 Amplified windshield mount antenna. It retails for slightly over $20. The antenna is mounted on the windshield with 3M tape right behind the rearview mirror and is virtually impossible to see once it is installed.
Aside from the antenna, here is what you will need to do this job:
1) Torx Screw driver
2) Wire Stripper
3) Phillips head screw drivers
4) Nut driver or sockets
5) Small adjustable wrench
6) A good body shop to fill in the hole and paint it when all is done
This antenna needs a power source that will provide power as long as the radio is on. This can be a bit tricky since the 2005 radio has power for up to 10 minutes after the ignition is shut off or one of the doors is opened. After much probing, I found that pin2 of the J1 connector on the Shaker 500/1000 is a very good source. (Shaker 500 pinout)
This pin provides power to the radio, so as long as the radio has power, so will the antenna. I ran the wires for the antenna down the a pillar on the right side. To remove the A pillar cover, just grab it firmly and pull away. It snaps in place. The shroud around the windshield is a bit trickier. First you need to remove the right visor which is held in place with Torx screws, and then just pull on the cover and it will come off. It is also held in place with snaps.
Clean the windshield with the provided alcohol swab. Remove the vinyl on the 3m tape on the antenna and mount the antenna as high on the windshield as possible so it will not be visible. Make sure the wires are pointed up so they can be routed under the windshield shroud.
There is a ground screw under the dome light assembly, back it out slightly and wrap the ground strap around it once and then re-tighten the screw. Now you can run the antenna and power leads along the windshield channel, down the A pillar and under the dash to the radio. (Hint: if you open the glove compartment box and gently squeeze the sides, it will fold completely out of the way giving you much better access.) Tie wrap the antenna and power lead to strategic points under the dash to secure the wires and make the installation look neat. You can reinstall all of the plastic shrouding, a-pillar and visor at this point and put the glove compartment box back by squeezing the sides and folding it back up
To tap into the radio lead , you will need to remove it. Start by removing the console, then the two trim pieces on the sides of the radio, and finally, unscrew the radio and pull it out. Remove the antenna connector and connect the new antenna. Cut the antenna power lead to size leaving a little slack (make sure you route it nice and neat, you may want to use electrical tape to integrate it into the existing harness. Strip a bit of insulation without cutting the wire on pin2 of the j1 connector (or use a vampire tap) and wrap the antenna lead around it. Wrap it with electrical tape. Now you can test your installation. If everything works, put your interior back together.
To remove the antenna, unscrew it from the base using a small wrench. Pop the cover off. There are three torx screws that hold antenna base in place. Remove the base. I could not find a way to remove the orange antenna wire. As a last result, I cut it off inside the fender, and as close to the firewall as possible inside the car.
Finally, take the car to your favorite body shop and have them weld the holes close, grind them flat, fill and paint. While they are at it, you might want to ask them to paint your mirrors also.