Hi folks! Just wanted to post about my sirius antenna installation. Before installing, I searched this and other forums for ideas because like many, I don't like the look of the antenna mounted above the windshield. There were several ideas for rear mounted antennas ranging from drilling holes in the roof to compromising the water tight integrity of the third light. After pulling the light off, I realized a rather simple way to install the antenna without drilling, and without the possibility of leaks. I hope this helps some of you out there!
What I realized, is that the third light has a very thin foam seal on the inside which is the only seal keeping water out of the cab. The rubber seals only hug the sides of the light. Some people said to allow the wire to go right across the top, and that the seal "should" form around the wire and prevent leaks... I don't believe that to be the case... water can enter a very tiny space, and the last place I want any water is inside the back of my headliner. So, after taking the light off, I saw a way to trace the wire around the top of the light, out of sight, and toward the bottom. If you allow the wire to cross the foam seal at the bottom of the light housing it is nearly impossible for water to get in (unless you have a pressure washer and aim directly into the bottom of the light housing... i.e. "it doesn't rain upward"). Anyway, here are some pictures that may help. The first thing I did was remove the tailight, leaving the wires attached. I ran the antenna wire down the large opening for the light and past the headliner so I could pull it down from the inside. The explanation of the pictures will be below each picture...
This first picture is with the light detached. You see the arrow pointing out the foam seal I was talking about. There is no rubber along the top of the housing. I used electrical tape to secure the antenna wire to the housing while working it around the light just to keep it in place. Once the light is mounted, the wire will stay put on it's own, but the tape makes things 100% easier for this process. You see the light hanging "upside down" so the tape you see here is along the top edge of the housing with the wire just inside enough to remain out of sight once mounted. Make sure to leave enough slack between the actual antenna and the housing for mounting on the roof.
This one is taken from the other side of the light housing after the antenna wire has been run around the side of the housing and along the bottom. Note the use of electrical tape along the bottom as well. In the very center of the light housing, at the bottom, is where the antenna wire will actually cross under the foam seal into the main hole where the housing mounts. So you can see what I mean by keeping the foam seal at the top of the light free from any obstruction, as water is more likely to leak down from the top rather than up from the bottom.
Here is the housing mounted back into it's spot with the tape from the top portion still showing.
Here, I used a razor blade to carefully cut and remove the visible portion of the tape.
This is the final location and look of the antena... leak free!
I didn't take pictures of the inside, but I chose to run the wire around the top passenger side of the truck. I ran it under the rear headliner, between the headliner and plastic trim on the sides, and under the black weather stripping around the top of the doors. The front door weather strip runs all the way down to the plastic trim piece just below the glove box which is a good place to rund the wire. I removed the lower glove box (four screws) and zip tied the antenna wire along the metal frame that holds the glove box in place. With the glove box removed, you can also access the side/top corner of the black plastic "cubbie" in the console below the A/C controls. This is where I mounted my receiver. I drilled a hole at the top corner of that black plastic cubbie large enough to run the antenna into it. You cannot see this hole unless you are on the floor of your truck looking into the console. It's a great place to discretely run the antenna wire. The wire is not visible anywhere in the truck. Make sure you just feed enough through to connect to your unit if you mount it here. Zip tie the rest behind the glove box bracket before you replace the glove box.
I'll see about adding some pictures of that final receiver location if anybody requests them.
I hope this helps somebody out!
What I realized, is that the third light has a very thin foam seal on the inside which is the only seal keeping water out of the cab. The rubber seals only hug the sides of the light. Some people said to allow the wire to go right across the top, and that the seal "should" form around the wire and prevent leaks... I don't believe that to be the case... water can enter a very tiny space, and the last place I want any water is inside the back of my headliner. So, after taking the light off, I saw a way to trace the wire around the top of the light, out of sight, and toward the bottom. If you allow the wire to cross the foam seal at the bottom of the light housing it is nearly impossible for water to get in (unless you have a pressure washer and aim directly into the bottom of the light housing... i.e. "it doesn't rain upward"). Anyway, here are some pictures that may help. The first thing I did was remove the tailight, leaving the wires attached. I ran the antenna wire down the large opening for the light and past the headliner so I could pull it down from the inside. The explanation of the pictures will be below each picture...

This first picture is with the light detached. You see the arrow pointing out the foam seal I was talking about. There is no rubber along the top of the housing. I used electrical tape to secure the antenna wire to the housing while working it around the light just to keep it in place. Once the light is mounted, the wire will stay put on it's own, but the tape makes things 100% easier for this process. You see the light hanging "upside down" so the tape you see here is along the top edge of the housing with the wire just inside enough to remain out of sight once mounted. Make sure to leave enough slack between the actual antenna and the housing for mounting on the roof.

This one is taken from the other side of the light housing after the antenna wire has been run around the side of the housing and along the bottom. Note the use of electrical tape along the bottom as well. In the very center of the light housing, at the bottom, is where the antenna wire will actually cross under the foam seal into the main hole where the housing mounts. So you can see what I mean by keeping the foam seal at the top of the light free from any obstruction, as water is more likely to leak down from the top rather than up from the bottom.

Here is the housing mounted back into it's spot with the tape from the top portion still showing.

Here, I used a razor blade to carefully cut and remove the visible portion of the tape.

This is the final location and look of the antena... leak free!
I didn't take pictures of the inside, but I chose to run the wire around the top passenger side of the truck. I ran it under the rear headliner, between the headliner and plastic trim on the sides, and under the black weather stripping around the top of the doors. The front door weather strip runs all the way down to the plastic trim piece just below the glove box which is a good place to rund the wire. I removed the lower glove box (four screws) and zip tied the antenna wire along the metal frame that holds the glove box in place. With the glove box removed, you can also access the side/top corner of the black plastic "cubbie" in the console below the A/C controls. This is where I mounted my receiver. I drilled a hole at the top corner of that black plastic cubbie large enough to run the antenna into it. You cannot see this hole unless you are on the floor of your truck looking into the console. It's a great place to discretely run the antenna wire. The wire is not visible anywhere in the truck. Make sure you just feed enough through to connect to your unit if you mount it here. Zip tie the rest behind the glove box bracket before you replace the glove box.
I'll see about adding some pictures of that final receiver location if anybody requests them.
I hope this helps somebody out!