Horn going off randomly (even while off)

[berndt]

I have a 92 convertible, and the horn just started randomly going off a few days ago. First thing I did was remove the airbag and look behind there. No pinched wires, and everything looks good.

Since then, I've realized a couple things:

1. The horn is beeping randomly (no long bursts) even when car is off. I cannot press the horn button to make the horn sound when car is off.

2. I pulled the fuse (#7) and that did not fix the issue.

3. I pulled the relay (K2) and that did not fix the issue.

The only thing that works, is to disconnect the battery entirely.

I'll probably get under the car tomorrow to just disconnect the horn(s), but I'm wondering if the community here has any ideas. Tracing electrical issues is not exactly my forte.

Thanks,

Berndt

[Seawolf]

If removing the relay doesn't fix the problem then there is a short between the power wire (Violet/Yellow) from the relay to the horn itself (not the steering wheel horn button). That wire must be shorting to a permanent power wire in the same section of the wiring harness, this is the only way the horn can get power if the relay is removed.

You'll need to visually inspect for this, wiggling that section of wire harness around might cause the horn to sound and give you a clue, but also check the wiring on the horn relay socket.

[IceWhite]

Does the car have an alarm? Could be the alarm has been wired to the horns, just my guess.

[berndt]

The car did have an alarm at some point, but there was a separate horn for that. I'm not sure what the previous owners may have done, though I'm sure it's playing a part.

Thanks for the hints about where to look for the short. In the mean time, I just removed the horns. That seemed like the easiest short-term solution.

[ELVA164]

Sounds like a short and/or a crossed wire causing the issue. I noticed you pulled the fuse for the horn relay, pulled the relay, but never pulled the fuse for the horn itself (27). You may want to give that a shot.



This reminds me of a prank I pulled in high school where I installed a jumper from a friend's right turn signal to the horn. Lulz ensued.

[Das Delfin]

sounds like a short somewhere. Look at the connector coming off the horn. Find the horns and trace the wires to where they connect to the body harness. Look for crumbling plastic or bare leads either on the horns themselves or on their connectors.

[Das Delfin]

Here's the circuit


This is a simple one so it's nice to beginners.

The right side (hot when run or start) only has power when the car is on so that side is most likely not your problem. The left side has power all the time so it's more likely that the issue is here and as such is a good place to start.

Our cars (most cars) have two horns, each one emitting a different sound and together they make a chord, which gives the horn its distinctive "fuck you" sound. What you want to do is listen and see if you can tell if the pitch is different when you honk the horn with the car running vs the sound you get when your problem is happening (when the horn honks itself with the car off). This will help us isolate the problem.

Of course, it's possible that when you honk the horn under normal conditions, one of the horns might already be disconnected. So if you have a friend with an e30 compare his horn to yours. If not, have a friend honk your horn (lol) while you plug your hears and stick your hand on each horn to feel that they are both vibrating.

This may seem like a lot of work but it's the easiest way to fix this without getting lost. Plus it'll give you a chance to check out your wiring and make sure it's in good shape without cuts or bare leads or w/e.

So my point being if only your high horn is acting up, the problem is with its wiring and vice versa. Makes it easier to trace.

My bet is it's possible the old alarm system was tied into the VI/YL (violet/yellow) wires and is randomly shorting to a previously used 12v. If you find a random wire connecting the two VI/YL wires that doesn't look like an oem connector, that's your problem. Cut the wire off and electrical tape any exposed metal (or shrink tube it if you can).

If there's no wire like above, then follow each VI/YL up through the loom wire until you find a disruption.

Lots of words so any questions lmk


fuse 27 is for the OBC horn (the buzzer when you exceed a set speed), not related

[berndt]

Mystery solved (mostly)

So it turns out, it's the factory alarm horn. I finally found a post:

https://s14net.vbulletin.net/forum/s14/general-e30-m3-discussion/1223128-horn-stuck-on-removing-relay-fuse-doesn-t-help

With pretty much the exact same symptoms. Pulling fuse 27 finally did the trick.

I woke up this AM to the horn blasting, and I didn't understand how that was possible as I REMOVED both car horns. Therefore, I figured there must be another horn somewhere. Finally I searched for "alarm horn", and that led me to the horn I was looking for.

I quickly tried to reset the OBC, but that didn't work (not sure if I did it properly). In the end, I just pulled fuse 27 and will deal with it later. This all started when my car was broken into and the batter ran down after the glovebox light was left ON for days and days.

[reelizmpro]

Do you use the OBC code function? The OBC horn is only supposed to sound after you enter a code and try to start the car a few times. If it's just randomly going off then you probably have an issue with the OBC relay box.

[berndt]

I don't use the code function. I'm going to pull the alarm horn. If I can find it.


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[berndt]

Finally pulled the horn. I had previously pulled the obc fuse, which solved the problem, but also disabled the power door locks. The horn is NOT easy to find! It's above the driver side regular horn, but hidden by a metal cover. The cover is held on by two screws and a plastic nut. The screws are accessible from above (behind the headlight). One is the screws is not visible, but I got it off with a 1/4" ratchet. There is another screw (same relative location) which actually holds the horn. Hopefully this helps someone!


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