Headlights and Horn won't shutoff
 

I just got 04 Mazda3 a few weeks ago. I just ran into a really strange problem. The horn used to act a little strange and stay on for a second or two when activated. Didn't think much of it, probably the horn relay sticking.

Anyway, just the other day the horn wouldn't stop after I slightly tap it. I had to disconnect the horn. This is where it gets strange.

The headlights and dash brake light (parking brake light) will now not turn off unless I remove the horn relay OR press the horn. Yes, pressing the horn turns the headlights off. Horn honks continuosly regardless if its pressed or not.

Anyway I tried a different relay and no change. So I just removed the horn relay and everything is fine other than no horn.

Any thoughts?

Sounds like a ground fault
 

If you have symptoms from multiple electrical/electronic systems, then there are only two things it could be.
Multiple unrelated problems, or a problem in the grounding system which is the only common component.
From the symptoms (Horn killing the lights) you give it sounds like this.
Unfortunately withthese, where the symptoms show may not necessarily be where the problem is. They can be a real pain to trace.

My '04 M3 just started doing the same thing yesterday. I went searching the forum to see if anyone else had the same thing happen to them. If I find out anything, I will let you all know. At this point, I'm thinking that it is a wiring short somewhere. I've got a feeling it's gonna be a pain to track down. I hope I'm wrong.

One year bump buuuuut.........did either of you ever find out where exactly the problem was? My wife's 05 Mazda3S is doing the exact same thing..... It started a couple weeks ago, the horn started staying on for a few seconds when pushed. Now, the horn doesn't work, the brake light in the dash is on, and turn signals/hazards/etc don't work..... The headlights work but if I push the horn, they shut off, along with the brake light in the dash. I also removed the horn relay and everything functions properly except the horn (obviously). Just hoping you guys tracked it down, I'd definitely appreciate any help you can offer in fixing this problem!!

I have not found out why my car is having the horn/headlight problem. I'm hoping to be able to spend some time next week while I'm on vacation to take a look at it. If I find anything, I will post it here.

Sweet--I'll post up any findings I come across as well......

So klawman, you've just been driving without a horn for the past year? Has it caused any other electrical problems? If this is a fix that is going to cost an arm and a leg, I was thinking about doing that as long as it wouldn't cause any other issues. Or maybe even wiring up a horn to a button.... :cool:

Has anyone verified their horn switch isn't actually stuck closed? Or that the horn relay is operating correctly? The horn connector is under the left side of the steering column, 8 pins, and two on the one end are the horn (the other end has a wire missing one in from the end). The car computer powering on with the horn engaged may cause some bug noone investigated (doubtful).

Looking at the schematics, it doesn't look like there's a common ground for enough parts to cause an issue. The horn ground is on the engine under the air intake - i've replaced mine since it was corroded - there were no failures yet.
I'm guessing there may be corrosion inside the passenger junction box control board it could short different systems together like this and cause issues. Corrosion between pins on the board could do this. I've looked at this board and I think it was coated, which would prevent corrosion. It's also sort of a pain to remove it from its housing.

I'm sort of lost to find a common connection for the horn, headlights, and e-brake indicator light. Thinking about it more makes me think there's corrosion or a bad connection in the passenger junction box (under the glove box). That contains logic to control all the systems effected (horn, cluster lights, turn signals) and seems to be the only common link I can see.

If any of you are around syracuse NY i'd love to help debug... as i'm sure my car will do the same thing in a few years :(.

lowrange93 - I have to give you a kudos for your WRX signature note. :nod: :laugh:

2005 Subaru WRX 18.5 psi of ticket-gettin' goodness

^^LOL thanks man!!! :bt:


Just following up on the problem--it was a bad pjb. I picked one up out of a junkyard with a warranty and got it programmed at the dealership and everything works great!! Everything except the horn did, that is. Turns out that the horn apparantly got fried--it went off in the middle of the night for ~45 minutes before the pjb got replaced(neighbors told me about it the next day--I never heard it). I threw in one of the old horns out of the Scoob (I took them out when I put in my Supertones) and everything's good as new.

Final cost--$333.19+one old WRX horn.....much less than I had anticipated.....hellz yeah

Glad it all worked out.
Any chance you kept the dead PJB? i'd be interested in seeing what is bad with it if you do.

there should be button or something to control that..maybe read the owner's manual. if it is an electrical problem, probably need to bring it to the shop

So I did a little troubleshooting last week on my horn problem. Yea, I know it's been a while since my original post. Verified that the relay and power lines going to it were ok. Verified the switched line going to the horn was ok.
Discovered that the ground side of the solenoid part of the relay was partly grounded out - about 180 ohms. Hence why the relay was always on. On the ground side of the solenoid, circuit takes two paths - one directly to the horn switch, and one to the anti-theft system. Verified that the ground side of solenoid going to the steering wheel horn switch was good. Verified the horn switch was good. Verified that the ground to the horn switch was good. Didn't have time to test, but I am wondering if the line to the anti-theft system (which is in the pjb) is bad? Will test and confirm as soon as I can. Good to know that lowrange93 had a problem with their pjb and fixed it. I will look at that (pjb) closely.

It was the PJB
 

Same problem as described above on my son's 2005 Mazda 3. Horn came on while he was driving home yesterday. Policeman assisted him by disconnecting the positive battery cable, then put it back on. After that, no horn, no turn signals, no power door locks, and the brake system light on the dashboard was on. In the garage at home, fooled around with it a bit. When the horn was depressed, a clicking sound from the PJB area, daytime running lights would turn off, and if I held the horn in, the turn signals and power door locks would work. I removed the Horn fuse from the engine compartment fuse box, and everything seemed to work, except the horn obviously. This morning when he went to leave to go to school, he couldn't get the car out of Park. Replaced the fuse, and back to the original problem, but at least I could get it into Reverse. I took it to the dealer today where they replaced the PJB and the horn. I believe their technical phrase was "your junction box was completely fried". I forgot to ask for the old one back, but will call tomorrow to see if they still have it. Technician wasn't much help when I asked what might have caused this, other than to say "it happens".

if you can get it back, i'd like it if you could take pics, or i'll pay for shipping - i'd love to see one that failed to see where the problem starts on these things.

I did get it back, but didn't get a chance to look at it yet. Nothing obvious from the outside, but I'll remove the screws and the cover tomorrow to take a closer look at it. Anything in particular you'd like pictures of?