Horn started blaring in the middle of the night. All on it's own. Went to turn it off by using alarm button and it didn't work. Panel lights flickered on and off when I turned the key. (Note: Heavy rain has been coming down) Electrical problem?

double posted. wow.
when it beeped, did you look in the display (RPM)
it tells you why?? the VFD or EVIC tells you why.? (rpm dial)
do you park with the alarm on , on the street or a garage?????
if in a garage park and turn alarm off. it does turn off the alarm.
did you bump the panic button?
eg its under your pillow?? LOL or the cat chewed it?
read your other post, it's got lots of answer there.
to find cause.
if the horns stays off, if alarm is off then its not the horn button.

as many will say. there are 4 things that run the horn.
button horn
alarm
door locks.
panic.(part of alarm but not totally)
on my car, i have most themn turned off, like the lamp flashings.
and the horn chirp is off on all my cars, all i get is the door lock click sounds, nice (neighbor friendly)
so turn all all that and see if the horn still fails.

that panic button can fail,
if mind did id pull the fob battery and then use FOB 2.
to see of the FOB fails.

your other post said driving
this one says, parked. 3am clue.

Sounds like a relay stuck on that killed the battery. I keep my parking lights on so I can see when the unit starts (no other feedback). Problem comes in when it starts and I don't know it, Parking lights come on and won't shut off till door is opened.
I think this is what killed my battery. I need to return to the installer and and have a relay installed so lights shout off when engine is off.
Hope this helps!!

Your horn relay may be shorting out, making your horn operate all the time. Have a look at your relays. You might find the horn relay is the same as another relay, If it is, try swapping relays with a known good one, and see if the horn operates normally. If so, get a new relay. Good-Day!

if you unplug the clock spring on the back side and the horn will stop then remove the air bag and check the switches and wires inside the steering wheel

In my case it turned out to be a bad horn pad on the steering wheel. It was especially bad when the weather was very cold. The horn would begin beeping in the middle of the night and wake me up, or begin beeping while I was driving. The dealership replaced it at no charge, so there must have been a recall for this problem. Good luck!

Is the alarm causing the horn to honk? If so, you need to figure out what is causing the alarm to trigger, which could be any number of things.
Or, the panic module could be failing.
It is least likely to be the horn ring unless the only way you can get the horn to stop is by "beating the horn button on the steering wheel".

If it is, then you can replace the parts for the horn button, but you will need to get an assembly manual for the vehicle. Be sure to disconnect the battery before attempting to remove the airbag module. If it goes off, then you risk injury, and, they are not cheap to replace.

I wonder,, with colder tempratures this time of year, If somehow a connection in the horn pad was shorting out.due to expansion or contraction of a component inside the steering wheel. Try tapping on the top of the air bag on the steering wheel and horn buttons ..this may work ..note this is a guess and I hope this does it the only reason I mentioned it Is because I have seen this two other times...Good luck.

if you follow instruction properly than the alarm should work properly, Go over your wiring again 2-3 times make sure it make sense to you with the instructions. If it make sense than take the unit back and get another, can be faulty alarm.

you will need a new horn pad behind the steering wheel.the tolerance is to close.