Nick, that small signal that you talk about, its called a HARMONIC. I've been in amatuer radio for 10 years now. I have to learn/know about that stuff before I can get my license.

Yes, usually. Again, I've had all 3 devices (Motorola Atrix, TomTom 340XL, and Garmin Oregon 450T used with success in the LeSabre. Its only once I move them to the truck, that things go haywire. And yes, the LeSabre has a modern Satellite radio setup with the antenna on the trunk lid.

One other item I have, and just thought to test it, is my handheld Midland CB. I can't even get a good signal with it. The background noise overwhelms the input level meter, no matter where it sits. I get a good amount of alternator whine through it as well. Completely useless.

The truck is the only variable here. All these other items work great in other vehicles, outside the truck, and even all turned on close together. I had the same setup when I was doing my geocaching in my LeSabre that I have in the truck, and it worked fine there.

If I knew for sure it was the sat radio, I would absolutely ditch the old setup and wire in a new dock and radio. I hate the "huge" sized interface taking up under seat storage space anyway. But, money is tight, and I really don't have extra dough to test a hunch. (Not for another 2-3 weeks anyway...)

You're talking to an ex Satellite Communications/Ground radio operator tech. I know all of what you're talking about.

That'* why I asked him distances of the devices.

given what you say about the cb, you may need better grounding or have an issue with spark plug wires

Yep, I totally missed that one. Read it too fast. I agree.

Been meaning to update this thread, but kept forgetting about it.

I did take the Sirius unit out, pulled the wires out that went to the antenna, and yanked the fuse on the interface unit. (I still have no idea where its getting power from, its ignition switched from somewhere....I hate undoing someone else'* aftermarket wiring...)

Anyhow, after that, I put my phone, Garmin, and the TomTom all in the truck, and went for a little test drive. I plugged in a few different places to go, and purposely drove in the wrong directions, just to see how well they would re-route me back. The TomTom was getting 100% or near that from the GPS satellites, and my phone showed a solid connection with an app called GPS status, and using google navigation, it also ran the same route as the TomTom, and kept making corrections quickly once I purposely went off course. Garmin was fine, as long as I kept it near a window. So, whatever the Sirius interface unit is doing, it is causing my GPS issues.
Put it all back together, and its back to not working. Guess I know the interface is the problem, either through some RF leak, or some other way, its the cause.

Rather than try and fix the older unit, and find out why, I'm just gonna yank the thing out and put in a modern Sirius dock, in the OH console where the old one is.
I have a feeling its gonna be a rough time tracking everything down. I have no radio at all when the interface is unplugged, and somehow the main control unit still had power. So its gonna be a lot of tracing wires back to find out just how this thing was installed, just to put it all back to normal.

I didn't hook up the CB, and see if there was a noise induced into the unit, with the interface shut down, but once I saw the TomTom getting consistent high satellite reception, I didn't really think to bother. It wouldn't surprise me if the interface was causing some crazy electromagnetic distortions in the cab. Even my portable weather radio had a tough time getting good reception.

Just thought I'd update y'all on what I figured out, since I know this was a sorta off the wall post.

Unlikely the CB would pickup interference from 2GHZ devices. CB sits between 26 and 27MHZ AM. CB'* are notorius for picking up DC motor/AC motor noise, lightning, powerline noise, ignition noise etc.

Mike, the Sirius unit has a built in cooling fan in the module under the seat.
Remember, this thing is the size of your average 200 watt audio amp.
This interface is ancient, compared to the newer ones. Who knows if its even properly grounded... I have signal drop outs from Sirius all the time with this, even in areas where a newer setup has no issues.
Something isn't right, but at least I know whats causing it, even if I don't know exactly why.

Well, when that unit was built, early 2000s I think, GPS and the like wasn't very popular except to those who had A LOT of money. So, therefore that unit might not be shielded very well.

To affect everything in the cab though, that'* a pretty big leak. I'm betting it'* not grounded right either by the sounds of things. Good luck on getting it all tore out and upgrading.