No radio reception?

Hello, so just looking at the OEM wiring really quick, your XM Satellite uses a different SDAR Antenna than the AM/FM frequencies, those frequencies use their own Antenna, and the OEM wiring shows a connector in-series from the Radio to the Antenna itself. There are 2 wires, one is just a shield pin 2 on the radio and the other is the signal pin 1. So it might be that this connector is either unplugged or corroded, broken etc. I'll see if I can find it for you and post the wiring diagrams as well.
Does the vehicle have an AMP?

There is a plug for the Radio, a plug at the antenna, but also another inline plug going to the antenna for AM/FM. The location for the AM/FM Antenna is on top of the vehicle slightly back correct? (2nd diagram)

You could try checking continuity from the Radio Antenna plug, and see if it has an open circuit with the antenna unplugged at the back of the radio.

It will show some resistance I'm sure, so check with the meter on a high resistance setting or auto, it does look like that connector is towards the back of the head liner.

Try the continuity check from the connector at the back of the radio first, see if it reads open circuit. I'd be curious to see what the resistance of an AM/FM antenna is.

Oh, I thought you had it out already, let me see if its overly complicated.

Here are some additional info on those cables, the xm and am/fm cables are coaxial that run together to the Antenna. Notice it has some routing info on them.

They actually have a flow chart for "Poor or no am/fm reception". Let me post that for you first, maybe you can figure this out without pulling the head liner down.

This flow chart has all kinds of adapters, you should be able to check the resistance without them, it's just a coaxial cable, the center pin is the signal pin and connector is the shield that runs through the cable around the center wire for interference purposes.
Diagrams 9, 10 are for the Radio removal, but these cables running along the passenger side floor, and up the C pillar, you may be able to find them in that area, because with pulling the radio, there's additional instructions on pulling the glove box as well. I'll post them too, but also check for any codes stored throughout the vehicle, have you done a full system scan yet?

Coaxial cables are almost always about 50ohm range, here are some additional info on this body verification test, this is all under the radio/antenna service info.

Okay, so, the actual Radio module itself is really behind the glovebox, and not part of the display if these diagrams are correct, so that should really simply things somewhat.

This is the audio setup with the Center Stack display, which is what it sounds like you're dealing with, this is considered the Premium Radio system 2. The 5th diagram is the Premium Radio system 1 (no Amp). The #2 system is very integrated, which includes the GPS Antenna along with the xm and am/fm antennas, and a lot more components.

Yeah, there's just so much integrated into the Radio system. But on the back of this unit, where they have the Antennas labelled with 1, looks really close to the module behind the glove box, for their resistance test, having you install a jumper, its most likely closing the circuit at one end unplugged and testing for a complete circuit. And out of the 3 Antennas, the AM/FM antenna looks to be the only one that changes colors after its inline connector which should make it easier to ID. I'm trying to find some easier way to locate this inline connector, there's just so much information here, sorting through it is taking a bit. The Antenna wiring runs under the passenger side floor I need to find this connector 1553A. The aftermarket coloring in diagram 4 is incorrect according to the OEM coloring. But I'm going to keep looking here.
Is anything setting codes?

Can you pull up the Antenna from outside to get to the wiring?

I would start with getting behind the glovebox, see if you can access the radio's main module from there. And then the antenna plug on the top left. There's endless codes that can set for radio faults or issues to do with that system. Go to the passenger side area where its most likely for the wiring or any connectors to have been damaged, start at the passenger side dash and work your way back. The C Pillar runs back along the passenger side to the rear door.