Atten: All Honda electrical gurus...

[Soichiro Jr.]

Hello. I have some questions. What would happen, if I replaced a 15amp fuse with a 20amp fuse in the oem underhood fusebox????

I'm asking, because I just bought a new horn(air) to put on my car('07 Si), but I've read that it(airhorn) blows the fuse in some Civics(some don't). This is what I've found out searching the web- the Wolo Badboy 419(my new horn) draws 12-12.5amps when first pushed(honked) then steadies off between 6-8amps while being continually pressed..... The horn fuse in my Si is shared with the stop lights and is 15amps. I've heard that the stop lights draw 5amps. That means that if I would step on the brakes and honk the horn(Wolo airhorn), the 15amp fuse protected horn/stop light circuit would experience a peak of 17-17.5amps blowing the 15amp fuse, correct? That is why I'm wondering about replacing the 15amp horn/stop fuse with a 20amp. Is there any way that a 20amp fuse would hurt the horn/stop light wiring? Could it hurt any other wiring or the fusebox????

I guess my other option would be to place a 12amp inline fuse between the airhorn and fusebox, right or no? Also, if I used 18 gauge instead of 16 gauge wire for the install, would that affect the amp draw on the electrical system? I've read of someone installing a horn using 18g wire, then replacing it with 16g wire and the horn sounded louder. Any real input would be greatly appreciated. Thank you very much. PEACE OUT!

[ryanmcm83]

Lol with 17.5A starting current for the airhorn coil and 5A for the horn you need a 25A or 30A fuse. If one of the parallel devices faults and you get a current surge it'll just draw from the ground at the fault point (if it hits ground that is, else u get nothing, just an open circuited dead device) and head upstream to the source, popping the fuse. The other device will just demand the same current until the fuse pops. Under fault conditions you want to protect the devices upstream. If the battery sees the fault it'll keep feeding current and heat up, not likely to blow though since it is only 12V and the wire gauges are small. The worst that could happen is the wire'll melt. The fuses are also meant to sectionalize the devices so if one device faults you won't open circuit all of the electronics in your car lol.
What could hurt other electronics are transient overvoltages from current spikes (due to inductance in wires. I won't explain more unless u really want a headache) but as long as their fuses are sized properly then no problem. If you were to feed a device directly from the battery, then it could be buh bye to that device if the battery sees the fault before the faulted line is cleared by a fuse.

Basically if your airhorn shorts and draws more than it's highest operating current and you tap your brakes you want to size your fuse to pop, but elsewise cover your bases and don't have it pop when you are drawing 17.5A and 5A after someone cuts you off and you jam your brakes and honk your horn while flipping them the bird.

As far as your wire goes, I'm not familiar with the small gauge wire ampacity ( I do high voltage power design as a profession) but it makes sense going to a bigger wire if others were having a problem with voltage dip. Going too big means your fault current will be greater if you do get a short to ground, but again that is why you get your fuse sized right! 25 should do. If it pops and everything is all right, get a 30.. They are cheap enough anyway.

I Hope that helps.

[dorkiedoode]

might as well start with 30amp and save some gas money.

[Soichiro Jr.]

Originally Posted by ryanmcm83

Lol with 17.5A starting current for the airhorn coil and 5A for the horn you need a 25A or 30A fuse.

Thanks for the input. But the airhorn starting current is 12.5A, not 17.5A and the brake lights are 5A. Together they are 17.5A; thats why I wanted to replace the oem 15A fuse with a 20A. I was just concerned about the use of a 20A fuse in a 15A circuit. My friend says that since it's only a 5A increase and since I'm not constantly riding the brakes and laying on the horn, that a 20A fuse should be ok on the horn/brake light wiring. I was just wondering what some knowledgable 8th members had to say about it. If there is any other can of worms I might be opening by using a 20A fuse instead of the oem 15A in the fusebox. Thanks again ryan, and also to anyone else who might chime in.

[bee-man]

I wouldn't recommend increasing the fuse size for the safety reasons mentioned. Hook it up the proper way by using a relay (fused). In fact, I can't believe that the air horn wasn't supplied with one!

[Soichiro Jr.]

Originally Posted by bee-man

In fact, I can't believe that the air horn wasn't supplied with one!

Thanks for the comments, bee-man. Yes the horn did come with a relay. The instructions came with 2 different ways to install the horn- 1.)"Electrical connections using vehicle's factory horn switch"(the way I want to do it) and 2.)"Electrical connections for using a new horn button switch". The relay is only used for the #2.) way of connecting the horn, but I don't want to have to push an accessory button to sound the horn; I want to use the factory steering wheel horn button. Can using a fuse rated +5A over the factory provided fuse really cause that much damage on a circuit that is only used intermittently? Or is that more reason to worry about it? I'm not trying to be a smart ass either. I really don't know. Please advise.

[bee-man]

Originally Posted by Soichiro Jr.

Can using a fuse rated +5A over the factory provided fuse really cause that much damage on a circuit that is only used intermittently?

No. Fuses are put in place to prevent damage in the event of an electrical short or faulty device. FOR YOUR APPLICATION, the worst thing that could happen is what Ryan mentioned - popping the fuse when braking and honking, which I hope doesn't cause the car in the back to rear end you. If you find that you have to use something larger than 30amps, then you are probably going to exceed the factory wire capacity, which could lead to melting wires in a worse case situation (braking, pulsing horn, 1 minute). I digress.

Correct instructions, right?
http://www.wolo-mfg.com/419%20english.pdf

Hooking up the relay is a little more cumbersome, but all your connections can be made in or near the engine compartment. I think Honda's are 2 wire at the horn - if so, you can execute Figure C. If not, then you'll have to follow Figure B, but the relay may need to be rewired depending on the active horn state. I can check on my car tomorrow if someone doesn't beat me to the punch.

Are you planning to disconnect your factory horns?

Good night.

[Soichiro Jr.]

Thank you very much for the input bee-man, I really appreciate it. Yes, those are the correct instructions, and I do plan on disconnecting/removing the factory horn.... On my car the wiring is only 1 wire at the horn, as it uses it's bracket for the ground. If you have time, check this thread for some very detailed pics> DIY - Replace your factory horn with 118db "Bad Boy" (39 pics)
I read the whole thread, and when someone mentioned the fuse issue, I became concerned. I'm not sure if the maker of that DIY ever added an inline fuse or not.... Another member put this very same horn on his (k20)8thcivic and his friend's(R18)8thcivic. His is fine, but his friend's blows(fuse) all the time. I don't have much experience doing electrical work(obviously), so I was hoping to do the simplest install possible. That's why I was thinking of installing it just like the DIY, except replace the 15A factory fuse with a 20A fuse in the factory fusebox. I know thats not the best way to go about it, but I figured; since the horn and brake lights are not constantly on, it should be ok(or not?). I just wanted to know if anyone has ever done this before(swap in +5A fuse), or if I'm a total idiot for even considering this.... My other option would be to add an inline fuse(12A, but horn draws up to 12.5A @start-up) between the horn and fusebox. I got those specs from another forum. I'm going to email Wolo to see if it's correct. Thanks again for your help. I gots to split. Take care.

[bee-man]

The link was very helpful. One wire means that the horn is active high (older Honda's were different). If simplicity is priority, follow the DIY link - Easiest, yes. Best, no. If you blow fuses, then incorporate the relay.

A knowledgeable installer would incorporate a relay for liability and performance - it isolates the airhorn from the car's main electrical system and avoids the skinny gauge factory wire for drive current. If you choose this route, just follow Figure C and connect relay terminal 85 to the horn wire, and connect relay terminal 86 to ground. That's it! When you press the horn, the relay will essentially make the connection from terminal 30 to 87... make sure you place the inline fuse close to the battery.

Also, if you plan to use the stock horn location, just know that you are likely violating instruction step #1. Oh, but I see you live in sunny San Diego.

Cheers.

[anavrin351]

The larger wire will allow for more current to travel throught it. The smaller the wire the more resistance there is. Resistance holds current back. The larger the wire, the better for current flow. But there is no need for overkill like going with 10AWG or something like that.

The fuse is there to protect the wire in the vehicle. If you hook up a larger fuse and draw too much current for too long, the insulation on the wire will break down and cause a fire over time. The wire hooked up to that fuse can only/should only handle 15 amps.

I would use the relay, or find an empty spot and add a fuse then take the horn wire out of its current spot and put it in the new slot.

[Rawhyde]

Save yourself a giant headache later on and use the relay in the circuit. Just use the factory horn wire to active the relay's coil. Make sure to use an inline fuse in the circuit before the relay's normally open contact.

[Soichiro Jr.]

Thanks for all the great responses bee-man, anavrin351 and Rawhyde. I think I'm gonna try the easy way first, but if I blow a fuse, I will install the relay ASAFP! I'll post up the results. If I blow a fuse, I may need one of ya'lls help for specific instructions on how to incorporate the relay(if it's not too much trouble- sorry bee-man & Rawhyde I still don't understand the relay wiring,lol). I really appreciate that all of you took the time to answer my questions, good sshhhhh.... Take care.



Edit: If I use the relay, I'll have to install a new "aftermarket accessory" horn button, correct? Or will I still be able to use the factory steering wheel horn button?

[Rawhyde]

You can still use the factory horn button if you install a relay.

[BigT]

Originally Posted by Soichiro Jr.

Edit: If I use the relay, I'll have to install a new "aftermarket accessory" horn button, correct? Or will I still be able to use the factory steering wheel horn button?

The instructions bee-man posted show exacly how to wire it with the factory horn button and a relay. As he said, follow Figure C and you should be good to go.

The factory horn wires will power the relay, and the relay will switch a power wire which comes directly from the battery to power the new horn. The only thing the factory horn circuit is powering is the relay. Your current on that circuit should be well below blowing the fuse.

The only wiring your really have to run is a power wire from the battery to the new horn/compressor.

[Soichiro Jr.]

Originally Posted by BigT

The instructions bee-man posted show exacly how to wire it with the factory horn button and a relay. As he said, follow Figure C and you should be good to go.

The factory horn wires will power the relay, and the relay will switch a power wire which comes directly from the battery to power the new horn. The only thing the factory horn circuit is powering is the relay. Your current on that circuit should be well below blowing the fuse.

The only wiring your really have to run is a power wire from the battery to the new horn/compressor.

Hello BigT, so let me see if I got this. I connect the horn power wire to terminal 85 on the relay. Then connect terminal 86 to a ground. (Can I use the same bolt that I'm hanging the airhorn on and grounding the airhorn on, to ground the relay with, or should I choose different grounding points for terminal 86 and the airhorn itself? Can they share the same grounding bolt?) Then I connect a wire from the "+" terminal on the airhorn to terminal 87 on the relay. The "-" terminal on the airhorn will be connected to the airhorns mounting bolt. Lastly, I connect terminal 30 to the battery's "+" terminal, installing an inline 20A fuse as close to the battery as possible. Is that correct???? Thanks again to everyone helping me out this is awsome, totally awsome! I love this site........... PEACE OUT!

[BigT]

Sounds like you have everything covered. And yes, you can use the same ground bolt for both.

Let us know how it works.

[Soichiro Jr.]

I'm installing the horn tomorrow...........

[benmunger]

Originally Posted by bee-man

I wouldn't recommend increasing the fuse size for the safety reasons mentioned. Hook it up the proper way by using a relay (fused). In fact, I can't believe that the air horn wasn't supplied with one!

relay, yup.

[Soichiro Jr.]

I'm here to report a great success! I couldn't have done this without the help of of my fellow 8th members that attended to me. Very big thanks to TigerDave, bee-man, anavrin351, Rawhyde and BigT for your input/answers/advice. I really, really, super heavy-duty appreciate it. If any of you are ever in San Diego, let me know; I'll do what I can to make it a nice visit.... I installed the horn using the relay switch. When the installation was done, I honked the horn, and it sounded nice and loud. Then I tried to arm the alarm using the key fob. The doors locked, but the lights did not flash and the horn did not sound. The dash alarm warning lights were not flashing either. After closing the hood and entering the radio code, everything worked as it should. I was so relieved! Also, I managed to remove the bumper without breaking any clips/fasteners. Thanks again to everybody that guided me through this! 8thcivic rules!!!!!!!!!!!!!