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2021 - Premium - Installing a Hella sharp tone horn kit - questions? (merged thread)

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8.3K views 51 replies 14 participants last post by  Cbick  
#1 ·
Vehicle Details:
Forester 2021
Transmission:
Automatic
Location:
Rangeley, Maine
So, the more I read the more I realize I might need some additional components to install my new horn kit. It looks like a harness and mounting bracket are essential. Can anyone verify that and tell me where I can purchase these items? I have a 2021 Forester Premium with and automatic transmission
 
#2 ·
I have a 2016 so YMMV but recently I installed hella sharptones. You may or may not need a bracket. I mounted both of my on the OEM t bar using a spare bolt and nut I had. Some companies make a relay harness but again, you don't necessarily need a relay harness but you may find the horns to be under powered without one. Not sure if the ones the companies make fit current model years. You can also make your own harness which is what I did.
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#4 ·
Ok. Where did you get the relay harness? And does how did you get around low power to the horn? Your schematic looks like you used the existing wires to the horn.
 
#7 ·
@DanPurcell I did a similar mod on my 2014 Outback. The idea is that you tap off of a wire going to a single existing horn. If you tried to 'drive' your new horns directly with the existing horn circuit, you would not be able to deliver sufficient amperage to properly operate your new high output Hella units. So you just use the existing horn wire as your "trigger". You can even leave your existing horns for additional volume and a clash of tones.

You run that trigger wire to the relay's coil circuit. On most automotive relays, that will be Pin 86. Pin 85 is the coil's ground connection.
Pin 30 is your new line to the battery that will power your horns. Don't forget to add a fuse to this line for basic safety! Your load, or new Hella horns will go on either Pin 87 or 87A. One of these is normally an open circuit (off), the other is normally connected (on). And yes, I've seen relays produced with marking swapped, so you might find you have to reverse them.

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#10 · (Edited)
Glad to hear this helped. @K675 did give you all that was needed, but sometimes the why part of electrical modifications need a bit more explaining. To me, the little pictogram/schematic that I showed above is poorly drawn, as one would expect the spring to be pulling the contact set away from electromagnet for the normally closed connection 87A, and energizing the coil should momentarily pull the contact home to make the connection to 87. I just checked in my "box 'o relays" and sure enough I have some drawn each way. So to the non-initiated user this can all be confusing.

You only need the 4 pin version. When you energize the replay with the existing horn circuit you want the replay to connect fresh battery power to your new horns at the same time (well, a few milliseconds later to be technical!).

The 5 pin unit gives you more options of having it disconnect something else that was always getting power. For the advanced user maybe operating lighting.

And yes, you just need to crimp two wires into the connector that attaches to pin 87, or create a pigtail so that you can feed new power to both of the new horns.
 
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#13 ·
Looking for guidance on adding a 12 v power wire to my battery. I assume it must connect directly to the battery post and that it needs an in line fuse. I havea 2021 Forester.
 
#15 ·
You may want to go with a fuse tap of some kind. This goes all the way to the fuse box and plugs into an existing fuse socket. You share that fuse socket with two fused items. Direct to the battery is not always a good idea.

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#16 · (Edited)
Sorry Dan, but there isn't an easy, straightforward answer to this question. Too many opinions out there, in part because I haven't been able to find an exact current load on most aftermarket horn options. I'll offer up this chart (one of many with slightly different values) as a guide:

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Let's assume that a pair of Hella horns draws 15 amps or so. The total wire length from the battery, tucked neatly out of sight down to the relay, and then on to horns and finally to ground is probably around 6+ feet or so. But now add some contact resistance loss due to the crimp connectors at the battery, into and out of the relay, and at the horns. I'd say you shouldn't be looking at less than 12 AWG stranded wire, but this is just a guess.

Any other opinions on this?
 
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#18 ·
What current draw for two Hella horns did you assume? Maybe I'm assuming way too great of a draw. What was the total wire length?
 
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#19 · (Edited)
It never hurts to go with a larger gauge provided the line is fused, and since the wire length is short, it's not like you have to buy a big roll of it. Get it by the foot at a hardware store.

Obviously, you don't need wire that would support a huge amperage load.
For DC applications, stranded wire carries current better than solid wire, and is easier to bend it around corners.

The popular version of the red horns is 5.5 amps according to the specs from Hella.
That means 14 AWG is more than adequate, but 12 or 10 AWG won't hurt, although it's a bit of overkill.
 
#21 ·
Hey Dan - what is it you're looking to power?

If it is inside the vehicle, I would go with "tap-a-fuse" solution as above - just find a powered fuse (key on or always on) and you've got juice.

If it's outside (auxiliary lighting, etc.), then you can do the same with the under-hood fuse box OR you can connect to the positive connector using one of those ring shaped electrical leads and connect at the bolt that tightens the cable to the post.

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Obviously, get one large enough to fit the bolt on the terminal.

Speaking of terminals - there are a variety of battery terminal "extension" devices that mount to the post and provide ways to connect to your battery.

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These may require the removal of the battery terminal cover - that red plastic cap on the positive battery post.

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#22 · (Edited)
Found the box, and used the part number to find the data sheet (although the basics were printed right on the box!)

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(Corrected! Tragic initial math error!):
So a load of two Supertones is 132 watts, or 11 amps nominal. So you should be using a absolute minimum of 16 AWG assuming minimized wiring length and no connection resistance loss. Add in a few crimps and connector/blade connections and I'd HIGHLY recommend 14 AWG as your safe choice.

What if you go with a smaller wire size?

1) Your load should be 98% of your voltage drop. If the wiring results in a greater voltage drop then you aren't getting the full blast from your horns. They may sound great to you compared to the stock horns, but you aren't getting all that you could. If you really did go 18 AWG, then the sound difference with better wire might be quite noticeable.

2) The 'Toaster Effect' comes into play. Your horns turn wattage into sound. Your wiring turns wattage into HEAT if there is more than a 2% drop. Generally a bad thing in electrical circuits, unless you are toasting bread or Pop Tarts.
 
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#23 ·
Sensors change on Subaru given the year. Our 2018 and 2019 have different arrangements. I don't know what the positive terminal looks like on your 2021. If it does have a sensor or fuse block, DO NOT connect on the BATTERY terminal side, as the electrical system uses these assemblies for load sensing. Always connect to where the other wires connect, not to the battery post side!
 
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#27 ·
Outstanding tech in this thread. I just learned that I've been running Hella Supertones incorrectly for about 23 years now. I need to go set them up right and see if they get louder! (They're already loud with the stock horn wiring). And @K675 that's some really nice wiring work!
 
#28 ·
For the record, wiring has a maximum voltage listing, but is rated by amps, not watts.
Unless you leave your horn on for extended periods, the worst that will happen is reduced volume.
No such issue with oversizing.
 
#30 · (Edited)
For the record, wiring has a maximum voltage listing, but is rated by amps, not watts.
Unless you leave your horn on for extended periods, the worst that will happen is reduced volume.
No such issue with oversizing.
Correct, but as an engineer I felt compelled to tell the whole story. Tomorrow we'll be neck deep in a discussion about driving lights....

1) Hella chose to state watts, leaving conversion to amps (necessary for determining wire size) to the reader. They include a relay in some kits, but not wire. They offer no recommendation on wire sizing that I have seen.

2) IMHO, 18 AWG wire is insufficient given the load and length discussed here. I stated reasons (performance and safety) why the OP should select something larger. The main issue in a case of a horn is performance. In this situation (a short duration on-time) safety is a secondary concern. But what better way to learn than to understand a wire sizing chart? I'll bet most of the folks here have never viewed one. A chance to understand. And the ability to download it for future reference for use in an application where safety really does come into play (and where fire can ruin the party).
 
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#34 ·
But what better way to learn than to understand a wire sizing chart?
A chance to understand
I agree 100%. I have seen hundreds of bad wiring jobs, incorrect wire size, God forbid no fuse on a lead hooked straight to the battery. I've seen melted wire, melted plastic, I've seen wire burn marks across paint. It's always a great time to learn the capacity of the wire you are intending on using especially if it is dealing with close to a couple hundred watts of power (Even if it's a temporary burst). It's also always nice to learn about resistance in connections, and what good and bad wiring connections are.
 
#36 ·
@DragonSubie7 I wasn't shooting at you (with my 12 gauge - I passed on the 20 because big = good in my book! ):p And I'm glad that you and @OuchDamn added details and support. And to @K675 for his photos/diagrams. To me, this is all second nature. Been playing with circuits since I was born, it seems. But that's not universal, so we need to do our part.

On the subject of Stranded vs. Solid wire: It comes down to a material science issue. I'm sure some will be wondering why the automotive chart seems overly conservative on length. I've also done home wiring, where solid conductor copper is preferred. Solid wires carry greater ampacity for the same gauge. NEC (National Electric Code) allows 14 AWG solid copper with a 15 amp breaker for 25 ft. That's in sharp contrast to the chart I posted for stranded wire.

But solid wire doesn't like to be bent around sharper corners as you need to do in the confined space in automobiles. Stranded wire also resists vibration fracture - a big issue in cars and rarely an issue in your home!
 
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#37 ·
Well, I think I'm going off a bit on a tangent, but there is a difference in ideal conductor configuration between direct and AC current.
The NEC is biased towards AC, and there are differences in recommended wire gauge between AC and DC.
Solid wire in AC can carry more current as there is more material to resist heat, but electron travel is different in DC.

DC needs to carry electrons throughout its length and also tends to be lower in voltage, so higher amps for the given power delivery (watts) means you need more surface area on the conductor than for AC, or it will heat up.
A lot.

In the low amperage levels under the hood, not so important, but in large scale solar systems (I've designed and installed several of them), the appropriate wire selection is critical.

In this actual example, a 30 volt 100 amp dc circuit for a multi-panel array will overheat a ~ 20 strand of 4 AWG, where a braided 4 AWG with ~ 200 strands will remain cool in the same application.
 
#38 ·
All true! I only brought it up to discourage anyone who has worked on their home from automatically assuming that wire is wire, power is power. If you can do a long run with 14-2 AWG Romex at home, why can't you do it on your car? The answer is BECAUSE....

And we haven't even touched on power factor corrections with AC circuits. I've had to do 3 phase primary power design in support of large high vacuum lab equipment installs, and UPS requirements to keep them up so that a safe, controlled power-down can occur. This stuff will come into play on electric vehicles depending on the motor choice! But now we are so far into the weeds that few following this thread will give a hoot!
 
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#39 ·
Yep -
Maybe folks who are interested have a bit more info, and I agree - At this point only the owls are likely to give a hoot.

For this thread, I doubt there is much more to say, but then, the answer to that question should be for the OP, also known as @DanPurcell ...
Sorry for the foray into the weeds.
Are your horns installed yet?
 
#41 ·
Yep -
Maybe folks who are interested have a bit more info, and I agree - At this point only the owls are likely to give a hoot.

For this thread, I doubt there is much more to say, but then, the answer to that question should be for the OP, also known as @DanPurcell ...
Sorry for the foray into the weeds.
Are your horns installed yet?
No. Car is in Maine and I’m in Virginia. Trying to gather what I can before I go there.
 
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