XM radio goes in and out

FM need a good antenna, buT FM in the country side will be weak
or even dead, FM does not travel far at all ,even only 20 miles
AM we have super power stations that cover most the country.
I bet the RADIO is just fine.
it can be bench tested with a 1 strand of say 4 feet of wire for an antenna.
you posted about only a RADIO not CD and not AM
FM is short ranged, 88 to 108MHz. is that
no town told , but you can call your closest station and ask them there coverage, spec.? 50miles or 10 or? what ever.
or you can go to a 2nd car, test FM see if there is one strong station.
if not there there is none.
on home RADIO we use a roof mounted 30Ft high antenna, FM
and goes way father,.
in car that can not be done, most antenna amps in cars only increase noise.
is this your first car, or first ever FM radio.?
yes antenna's can fail even the ground, (it is 2 wire coax to fail)
the mount can corrode. the cable can be bad.
some have antenna in the wind shield glass, and some one puts in new glass with no antenna there well that fails hard.
FM is mostly a CITY BIG DEAL, no living in the sticks.
also there are tiny FM micro station,and those are weak.
only line get a FM map for you town, just like Cell phones but for FM.
radio. see what is there and its POWER/coverage.

These are the three top websites. According to Just Answer it came with AM/FM Radio, AM/FM Radio Cassette, and two types of AM/FM Cassette / CD Changer. All 4 are shown in the link

https://www.justanswer.com/ford/0hkix-find-1999-ford-taurus-stereo-wiring-harness-diagram.html

These are the other two websites.

1999 Ford Taurus Car Stereo Wire Colors and Locations

The12Volt https://www.the12volt.com > installbay > stereodetail
1999 Ford Taurus Stereo Wiring ; Ground, Black/Light Green ; Illumination, Light Blue/Red ; Dimmer, n/a ; Antenna, Left Rear ; Front Speakers, 5" x 7" Doors.

1999 Ford Taurus Radio Wiring Diagram

MODIFIEDLIFE https://www.modifiedlife.com > 1999-ford-taurus-radi...
Our 1999 Ford Taurus radio wiring diagram shows you all the radio wire colors and what they do. Table of Contents. 1999 Ford Taurus Radio Wiring Diagram; 1999 ...

.. Here is the AM/FM Radio wiring

If you can get access to under the antenna check that the wiring plug is fully inserted.

Do you have base or up;level system ?

Table 1: Radio Features
Table 2: Cassette Features
Table 3: Compact Disc Features
Table 4: XM Advisory Messages
The radio receives power from the RADIO fuse in the junction block-right I/P. Ground is provided via G201 and G202. The radio is enabled/disabled by class 2 messages from the body control module (BCM). The radio routes audio signals from the digital radio receiver or the vehicle communication interface module (VCIM) to the speakers and/or amplifier when directed by class 2 messages.
The Entertainment System on this vehicle is configured with an AM/FM stereo radio with the radio data system (RDS) and either a cassette player or a CD player or both. CD and cassette. The uplevel system provides the customer with extended range speakers and an audio amplifier. Satellite digital radio (U2K) is available with uplevel systems.
The following list shows the radios available for this vehicle:
• Radio (ULO) - AM/FM Stereo, Cassette with RDS
• Radio (UNO) - AM/FM Stereo, CD and RDS
• Radio (UPO) - AM/FM Stereo, Cassette with CD and RDS .The complexity of the radio systems on these vehicle is mind blowing .

Your best bet take it to a GM dealer , has features you are unawear of .
DTC B1025, B1035, B1045, or B1055
When the radio is powered up, the radio supplies low level audio signals to the speakers. If the vehicle is equipped with an audio amplifier, the amplifier will boost the signal sent to the speakers.
DTC B1025 Audio Output Circuit
Install a scan tool.
Turn ON the ignition, with the engine OFF.
With the scan tool, monitor the DTC Information for DTC B1025.
Does the scan tool indicate that DTC B1025 is current?

Troubleshooting the problem may depend on which of several radio options is installed in your vehicle. However, the most probable cause is the antenna. Two different antennas are involved here - one for XM (satellite), one for FM (terrestrial - window type). To start, I would check the FM antenna connections at the window and the radio and the cable between them. If that isn't the problem, the radio is probably faulty.

are all the radio function dead.?????
what are they, radio, AM and FM dead, cassette, CD,?
if only the radio is dead. (static) then the antenna is bad or its lead in coax wire is bad. or fell off. etc.
the amp (audio is good) as you heard the static.
you can unplug the antenna, wire, from radio and plug in any
lenght of wire to test the radio, any radio can be bench tested this way. and is in any shop.

its very rare today for any head end radio unit to be only a radio.
so do the other features (other audio sources work?) try them.
if they work then the antenna is bad.

a new radio?, or used, make and model # , must i guess?
all modes on the radio dead, AM/FM,CD/USB/IPOD jack
ALL, that be the first tests and if all bad that means you lost power.
does the radio scan? show signs its trying? when asked, LCD live? or dead. all i know is the word PROBLEM (vast possible)
did you ask the maker of said radio.
did you follow the new radio's instructions sheet.?

disconnecting the battery, wow !

the radios can have 3 or 4 power pins.
1: Radio power (head end power)
2: dial light (goes to car park dimmer)
3: some have a memory wire, if not connected all programming will be lost. this must go to HOT ALL TIMES line.
4: electric antenna, (it's an output but is power)]

and at least 1 good speaker connected.
and for AM/FM any test antenna or just a wire 12ft long works.
the radio can be bench tests.
1 battery 12v
1 radio
1 speak or 2.
1 antenna. now can test for days like this..... anyone.

I am not sure about repairing the unit. Do you have a CD cleaner?
You might check with a reputable auto electronics shop, one that specializes in car audio. They may have an adapter that will allow an aftermarket radio to be controlled from the steering wheel. Rosen makes a nice am/fm/cd/dvd navigation unit that also has XM and iPod inputs. The hard part will be to find supporting interfaces and wiring harnesses to fit a 99.

this usually is caused by either a defective antenna ground to the chassis of the car or a defective antenna or antenna lead to radio.