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
DanPurcell
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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.
![Image]()
These may require the removal of the battery terminal cover - that red plastic cap on the positive battery post.
![Image]()
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.
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.
These may require the removal of the battery terminal cover - that red plastic cap on the positive battery post.
Found the box, and used the part number to find the data sheet (although the basics were printed right on the box!)
![Image]()
(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.
(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.
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!
@DanPurcell what are you attempting to hook up?
Join the fun: ('19+) - 2021 - Installing a Hella sharp tone horn...
We've beaten the subject of relays to death, and are now into wire gauge.
This discussion really should be moved into there.....
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.
Unless you leave your horn on for extended periods, the worst that will happen is reduced volume.
No such issue with oversizing.
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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).
Funny. I thought it was old person, also me!😁Original Poster i.e. you
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.
Some electrical specs don't include amperage, so it's a good idea to know how to calculate it.
How to derive amps from watts was not mentioned...
It isn't complicated, and will be applicable to any wiring projects.
As you well know, but perhaps some others don't, if you have the wattage spec you divide by the system voltage (in this case 12) to get amps.
Amps = Watts / Voltage
I agree with you and didn't state otherwise.
Another consideration is the conductor material, which should be copper, and the conductor configuration which can be solid wire, braided or stranded.
In DC current applications like under the hood, braided or stranded are better than solid, as electricity is actually carried on the exterior of the wire, and the more individual conductors, more current can be carried with less heating and voltage drop.
This is overkill with horns, as they are only on for short periods, but for continuous high wattage / amperage accessories like lighting, or any application with a large current draw, choosing a braided or stranded wire of an adequate gauge can make a positive difference.
In applications like solar power, these multi-conductor types are essential.
Also worth restating is something you also know, but some may not, is that it doesn't hurt to use a larger gauge wire, which is a smaller gauge number - 10 AWG wire is larger and carries more current than 12 AWG.
Apparently the wire standard uses shotgun logic.
@DragonSubie7 I wasn't shooting at you (with my 12 gauge - I passed on the 20 because big = good in my book! ) 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!
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!
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.
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.
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!
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!
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?
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?
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