Mi lincoln ls 02 horn is not working the plug has the 12 volts

suggest checking if 12 volts goes to horn wire at horn end when horn pressed from inside vehicle. A 12 Volt probe {google it} can be a cheap checking tool for this.
If 12v volts is switched when button is pressed {could be earth being switched if it is then place probe on constant 12 volts and negative lead on switched earth wire} then the horn itself is faulty.
If no voltage switched then horn relay needs to be checked. check if voltage at horn relay coil contact when button pressed.
if yes then relay may be faulty. if no then horn switch could be faulty.
you can check switched voltage also at horn relay switched contact when relay plugged in. To see if relay is doing what it is meant to do

What is the problem with the horn. Check Fuse for Horn. Check Horn it is located under the bonnet. Near the front grill of the car. Check relay for horn most likely also located somewhere in engine compartment in a plastic box compartment with numerous relays. If horn not sounding should hear relay click when horn button pressed.
If horn is getting voltage at horn plug (positively switched horn design) then horn may need replacing.If negatively switched then horn connects to body of car when button pressed and other side of circuit has Plus 12 volts always on it.

Knowing the MY (model/year) tells me the horn is the problem. Yet, there is a Horn Relay and a fuse which feeds it power. A simple test with a 12 volt light bulb can verify/eliminate this as the cause. Connect a bulb (12 volt) to the connector contacts which plug into the horn. Then activate the horn (press on the steering wheel airbag) to see if the bulb lights up. If it does, then it's the horn. If it doesn't (make sure the bulb and connections are good), then the problem is in the wiring/relay/fuse.

easy check first ,, you need help,, disconnect the 2 wires at the horn itself, Located by the front gill under the hood,, use a multimeter to check for power,, have someone try and honk the horn to see if the horn itself is receiving power, if it is,, the horn went bad, if not,, the contacts in the horn contacts are bad, which doesn't happen often but it does happen, or ( and I don't know on your model, ) you may have a horn relay thats not working, I'll check more to see if I can locate that answer

Put 12 volts to horn. If it works
then the horn button

Check fuse, if ok have somone use a volt meter while you depress the horn, and see if you are getting 12 volts, if you are not and the fuse is good, then it is the relay, if you have 12 volts to the horn wire, then the horn is bad.

If you have access to a volt meter turn it to dc volts and unplug the horn have some one activate horn while you check the volts. should have around 12volts. If you do its the horn itself.

check the battery junction box i think that will be the reson for all these problems to happen together

Good/best, place to start looking.

When you press on the horn button do you hear the horn relay click? The start at the horn, bench test it, if it works then check for power, is the fuse good and is the relay ok. If the stuff checks out then it may be the horn contacts behind the steering wheel.