SOLVED: Horn Relay + Fuse keep blowing (V70, 2004) Topic is solved

crimsonv70 · Post by **crimsonv70** » 28 Jan 2025, 01:07

Hi folks!
So glad this community is still here- I lost my login for a while but I my volvo!!

So I was being a bit irresponsible with some friends over the new year and was honking my horn a bunch. It blew the 15A fuse.

The trouble is, it blew the relay as well. I replaced both and....It blew them up yet again.

Any ideas what I could check? Seems to be a strange electrical issue. (FMI2 and fuse #9 are what keeps blowing)

Note, I'm very skilled at surface mount PCB repairs and soldering, so that's not a barrier.

Hamburger · Post by **Hamburger** » 28 Jan 2025, 01:25

Without further research, your horn has honked its last honk....

try another horn and i think you should be good.

Post by **jonesg** » 28 Jan 2025, 10:49

disconnect the horn/s from their power feed, replace the fuse and relay, if the fuse pops again its not the horn.
I would suspect the steering wheel. You were over enthusiastic with it.

crimsonv70 · Post by **crimsonv70** » 28 Jan 2025, 17:31

Thanks for the replies

To clarify:

1. The fuse and relay blows if I honk the horn a few times (it works fine if I honk once but not twice in succession)
2. After the fuse and relay are replaced, the horn honks. It works fine unless I honk twice in succession... If I do that (easy to do), it will blow the fuse and relay again.

What could it be in the steering wheel? I'm at a loss to understand what would electrically be causing this.

Post by **jonesg** » 28 Jan 2025, 20:17

the horn switch is in the steering wheel.
If its integrated into the airbag module clockspring it can get expensive, I'm seeing $180+ part and the steering wheel has to come off.
I would run my own wiring and a momentary button, $15 vs $500 in a shop, you probably only really need it to pass inspection.

crimsonv70 · Post by **crimsonv70** » 29 Jan 2025, 01:43

jonesg wrote: 28 Jan 2025, 20:17 the horn switch is in the steering wheel.
If its integrated into the airbag module clockspring it can get expensive, I'm seeing $180+ part and the steering wheel has to come off.
I would run my own wiring and a momentary button, $15 vs $500 in a shop, you probably only really need it to pass inspection.

Yeesh, thats expensive.
I just dont see how closing a switch for the horn would blow a relay though? Especially if it's only closing it twice in succession. There must be something else going on, although I'm not sure what :/

wiring diagram attached but it's strange - a lot of custom symbols here. and how is the relay getting activated by a single high voltage (30v) source without ground(?)

Post by **jonesg** » 29 Jan 2025, 09:53

you broke something in the switch or one of the 4 switches (3/37),
press it once and it sticks, press it again and it shorts out.

I'm pretty sure you can find a used one on ebay, then you either have to install it or pay a shop.
Its difficult to tell from the diagram, it might be integrated into the airbag module or can be disconnected, if its seperate thats cheaper than an all in one integrated module.

Watch some videos to learn how to access, disconnect the battery first.
The querstion I can't answer is whether the horn switch is in the airbag part or is it under the steering wheel with the steering angle sensor, if its part of the airbag module you don't need to remove the steering wheel.
If you call FCP the techs can tell you one way or the other.

crimsonv70 · Post by **crimsonv70** » 01 Jul 2026, 14:15

jonesg wrote: 29 Jan 2025, 09:53 you broke something in the switch or one of the 4 switches (3/37),
press it once and it sticks, press it again and it shorts out.

I'm pretty sure you can find a used one on ebay, then you either have to install it or pay a shop.
Its difficult to tell from the diagram, it might be integrated into the airbag module or can be disconnected, if its seperate thats cheaper than an all in one integrated module.

Watch some videos to learn how to access, disconnect the battery first.
The querstion I can't answer is whether the horn switch is in the airbag part or is it under the steering wheel with the steering angle sensor, if its part of the airbag module you don't need to remove the steering wheel.
If you call FCP the techs can tell you one way or the other.

Thank you Jonesg for the replies!

Good news -- I got it fixed finally!! My mechanic actually was a huge help in diagnosis (and a couple online videos

)

Turns out my 2004 V70 (and most volvos) have 2x horns (!). So what was happening was 1x of the horns broke (shorted) and that lead to a partially working horn sound for a short while until the fuse and relay blew up.

There is a neat trick my mechanic showed me for reaching the horns Vadis / dealer says you need to take off the entire bumper, but this is not so.

1. pop the hood
2. remove 6x black push clips on the top of grill area
3. bend the body of the car forward over the frame. You might want to remove the nuts on headlight wipers if you have those first
4. use a flat head or pliars to undo the 4x metal spring clips holding the top of the grille in place (NOTE: the grille is ABS plastic, not metal! even though it looks metal. You may need to epoxy clips if they break - I had to fix 2).
5. after those 4 clips are removed, carefully hold the grille towards you and undo the bottom 3 clips the same way
6. remove the grille and carefully set aside
7. you will see the 2x horns now. there is a 2-wire plug to each, with a metal slip around it. Push in the metal clip and pull on the plug to remove. The clip needs to stay pressed down to unplug.
8. measure both horn resistance. Mine were 0.7ohms and 1.1ohms on a crappy DMM meter (so likely not super accurate). The 1.1ohms one was actually the dead one.
9. unplug both horns and test the horn for a "click" in the relay. Make sure fuse #9 is in place (15amp) and relay FMI12. Even if the car is off, you should hear an audible click when the horn button (steering wheel) is pressed
10. now try plugging in the horn (only 1x) with the lowest resistance. Press horn once. Dont hold the horn, just a tap (we dont want to blow the fuse)
11. Do the same to test the other horn.
12. If no sound for either horn ever, you might have a wiring issue. There is a plug under the hood that both horns go to (one of the youtube videos shows that plug was loose). but first you can maybe have a friend hold the DMM for you on the horn plug while you press the steering wheel to see if voltage is coming through. Or use DMM hold function or you can maybe get creative with a 12V light bulb

Horn is cheap (abour $20 on ebay at time of this writing). Make sure to save your "L" braket though, those vary!
Horn part #0055306

Video I made:

Below are the videos that helped me, even though my technique was a bit different:

Have fun honking!!