2004. Why did it suddenly lose power?

You didn't say year or make. Some vehicles have a relay

trace wires to find the short

1st - check your relay box for water / foreign matter...
2nd - Is the horn relay working in conjunction w/ horn?
3rd - Is the park lights relay working in conjunction w/ park lights?

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You need to buy a repair manual for the car and in the back of the manual is a wiring schematic. I would start by finding what else runs on the radio fuse besides the radio.

Make sure that the wires are grounded. One should be connecting to the horn itself, while the other one should be bolted onto the car nearby. I had this exact problem with my '03, and I felt like such an idiot when I finally figured out that my second wire wasn't grounded

What year is the vehicle ?

They are talking about the body control module, but I'm not sure they are right. The horn does not need the bcm to work. See diagram below. The horn relay is energized by the horn switch on the steering wheel. The switch also signals the bcm, but that is not used to power the horn.


The turn signal does not use the bcm at all. The problem there may be the switch or the wire. See diagram below.






The instrument lights DO REQUIRE the bcm, but can be rewired to bypass the bcm. The gray wire from the bcm in the diagram below powers the instrument lights. You can cut the gray wire and splice it to the brown wire from the multi function switch. Find the brown wire coming out the bottom of the steering column, skin some insulation off the wire and verify it has 12 volts when the parking lights are on. Do not cut the brown wire--just attach the gray wire to it. You will not be able to dim the lights, but they will come on.

check fuses first step. if o.k. check power at radio-12v. horn &air bag may be related .airbag system needs checked by a pro. test fuses / test light or ohmmeter.

Double check the fuses. Also, there are usually TWO fuses for the radio. One has power when the car switch is OFF. This keeps the clock working and your radio presets set. The other is when you turn the key on. The horn not working can be tested if you have a 12V test light (Wal*Mart sells them...). Unplug the horn, hook up the test light, press the horn button. If the light glows, you've got a bad horn (go to your local junkyard for one). If not, recheck ALL the fuses. Good Luck

horn is usualy located behind the grill pull the wire off the horn using a
test light have somone push the button + check wire for power if theres
power try using a jumper wire to put 12v to the horn if no toot bad horn
I should have said check fuse 1st but do that if no pwr at horn wire
if the fuse is good and the horn works with the jumper most likly the
horn button is bad. hope this helps good luck