3rd Generation Specific (1993-2002) 1993-2002 Discussion including performance modifications and Technical Support Sections.

Horn constantly going off?

Old 09-25-17, 06:22 PM
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Horn constantly going off?

Hey guys, I did some searching and most issues with the horn I have found are either horn not working (which the FSM describes the fix) or that it is tied in with the alarm system, as in headlights going up and down, try to lock and unlock car, etc.. to fix it. Well here is what has happened... (94 PEP)

Everything was working fine until today, I installed the Pettit Racing air pump delete kit, and a heated O2 sensor, as well as some R1 Oil Coolers, when I put the battery back in, the horn started constantly going off. Not pulsing, no headlights flashing, no alarm light, nothing that would say it is alarm related. Just constant horn.

I only had one horn so I switched it to the passenger side plug and it still is happening, I tested the horn relay by running 12v to the 2 smaller contacts inside it and could feel and hear the relay switching. Hitting the horn on the steering wheel doesn't seem to do anything (hit it to see if the switch needed to be unstuck or something, haven't touched it since IDK when, never use the horn). I see that the horn grounds itself through the mounting bolt and only needs the one hot wire to connect it.

I wouldn't really give a damn but I need a working horn to pass NC safety inspection for registration.
Looks like a brand new CPU 1 and 2 will be around 350 bucks. Hope I don't need to spend on that, though new ones may be a good thing...

Any thoughts? I appreciate the help.

Last edited by b3delta; 09-25-17 at 07:48 PM.
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Old 09-25-17, 08:08 PM
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Mine did the same thing when my CPU#2 took a crap, have you try disconnecting it?
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Old 09-25-17, 08:13 PM
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Disconnect CPU2? I pulled the relay to turn off the horn.
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Old 09-25-17, 08:36 PM
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Yup, my CPU#2 is permanently disconnected. Something inside of mine probably shorted, the horn will just go off non-stop. I can remove the relay but then I won’t be able to use the horn, without the CPU#2 I only lose the alarm, which I don’t use anyways.
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Old 09-25-17, 09:03 PM
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Interesting, anything else happen by disconnecting the CPU? is it the whole thing or just one plug on it?
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Old 09-25-17, 09:47 PM
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There are 2 plugs, one 20 pins and one 8 pins. The 8 pins has something to do with the factory alarm, which I think is what causing my horn to stay on, disconnecting the 8 pins connector will only affect the alarm.
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Old 09-26-17, 10:17 AM
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Disconnected the 8 pin connector on CPU 2 (the one on the bottom) horn still going off. ugh....
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Old 09-26-17, 10:46 AM
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popped the hazard fuse, replaced, still constant horn, with or without 8, 20 pin, or 16-20 pin black above CPU2 plugged in

just pulled the airbag, horn going off even with steering wheel horn switch disconnected (at the airbag, Nardi steering wheel)

Last edited by b3delta; 09-26-17 at 11:53 AM.
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Old 09-26-17, 01:02 PM
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Unfortunately you're probably not going to have an easy time finding this. The horn wire is shorting to ground somewhere and it's making it go all the time.

Check the fender liners to see if the wheels rubbed through the liner into the harness, when that happens you get a world of weird stuff electrically.

Dale
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Old 09-26-17, 02:06 PM
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Yup, you have ruled out the security system, now it’s time to trace the wire and see where it got shorted.
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Old 09-26-17, 02:15 PM
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I appreciate the help guys, Just pulled the Intercooler and its working correctly now, now to find the wire in that pile of crap....

edit: found it. it was the green and orange (maybe red) wire located in the front harness. The bolts that hold the IC in place were really long and had been pushing into the harness. Taped up the problem wireS, there was a larger blue and red wire that had some exposed wire as well, switched to some shorter bolts for the IC and problem solved.

Thanks for the help, new relay on the way....oh well, now i'll have a spare.

BTW is there a wire in that front harness that affects the tach? my tach only works when its really hot out (like 90 or higher) and the car has been sitting in the sun, makes me think expanding metal somewhere makes a connection to work.

Last edited by b3delta; 09-26-17 at 02:46 PM.
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Old 09-26-17, 08:29 PM
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The only thing that is in the engine bay and relevant to the instrument cluster is Ground Point #3. Refer to the Wiring Diagram Manual, Section C-1, Pg C1-3 (PDF Pg 5). The ground signal leaves Pin 1E from the Instrument Cluster thru X-17 to X-14 [X-07 then to X-14 for Auto Trans] and finally to Ground Point #3 on the Emissions Harness.

If GND is loose then you would see all kinds of crazy stuff on the instrument cluster. If the tach is only affected then you should troubleshoot the tach/speedo circuit board. There are a few relevant threads for that.

Cheers,
George
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