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I have a 2016 Corolla LE. I want to replace the OEM horn with the Wolo Maxi Sound model 320-2T (high and low tones), each horn draws 7 amps for a total of 14 amps. Wolo’s installation instructions state it is important that there is a 15-amp fuse in the horn circuit. My corolla came with a 10-amp horn fuse and a 20-amp Denso horn relay. Question: If I install a 15-amp horn fuse, will the current fry the wire from the relay to the horn(s)? I cannot find information on the AWG size of wire. From inspection it appears very thin, 18 AWG to 20 AWG maybe, and its length from relay to horn is from three to six feet. Question: What is the size of this wire? I note that high end Toyota cars which have two horns are equipped with a 10-amp horn fuse. Question: If I install the Wolo horns and leave the 10-amp fuse in place, what is the probability of blowing the fuse? Thanks for any help.
 

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09 Corolla Base 17 Camry SE
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I have a 2016 Corolla LE. I want to replace the OEM horn with the Wolo Maxi Sound model 320-2T (high and low tones), each horn draws 7 amps for a total of 14 amps. Wolo’s installation instructions state it is important that there is a 15-amp fuse in the horn circuit. My corolla came with a 10-amp horn fuse and a 20-amp Denso horn relay. Question: If I install a 15-amp horn fuse, will the current fry the wire from the relay to the horn(s)? I cannot find information on the AWG size of wire. From inspection it appears very thin, 18 AWG to 20 AWG maybe, and its length from relay to horn is from three to six feet. Question: What is the size of this wire? I note that high end Toyota cars which have two horns are equipped with a 10-amp horn fuse. Question: If I install the Wolo horns and leave the 10-amp fuse in place, what is the probability of blowing the fuse? Thanks for any help.
Just changing the fuse to a 15 amp is asking for trouble. On my 09 the horn wire was 20ga at most. Use a relay and be safe.

Here is a wire chart I found and posted before. Happy to share it again.
http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/
 

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You can use the existing horn wires to power the relay and that is a good location to put the relay, but you will need to run a decent sized cable from the battery to the location of the new horn (via the relay) and then have a separate ground for the horn.
There are wiring kits you can get for this that help - Wolo makes them too - and they include a fuse.

You were right to be cautious about the car wiring, they make the wires just big enough to carry the expected current now - weight and cost savings supposedly - so don't overload them.
 

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Discussion Starter #4
Replacement horn issue

I prefer not to add another relay and do extra wiring.

The referenced wiring chart (“12 Volt Wiring Gauge Requirements at specific Amps for Automotive Electrical Systems”) indicates that a ten-foot length of 18 AWG wire can safely (?) carry 15 amps at 12 volts. The size of the wire from the relay to the OEM horn is probably 18 AWG and measures between three and six feet, surely no longer than six. So, it should be able to handle up to a 15-amp draw with “normal” usage, that is, for short blasts – not laying on the horn button for minutes.

But using an “Automotive Wire Size Calculator” (http://www.gtsparkplugs.com/WireSizeCalc.html) I determined:
(a) 18 AWG wire no longer than 4.32 feet should be used to carry 10 amps at 13.8 volts (2% voltage drop).
(b) 18 AWG wire no longer than 2.88 feet should be used to carry 15 amps at 13.8 volts (2% voltage drop).

A tech representative at Wolo Horns told me that with “normal” usage each of the two horns draw about four amps, total of about 8 amps. Nevertheless, he said I should use a 15-amp fuse with the set of Wolo Maxi Sound horns. But if normal use draws 8 amps, I guess it would be OK to use the 10-amp fuse. If I stick with the OEM 10-amp fuse, will it decrease delivery of the full potential to the horns?

I want the full potential but I don’t want to burn up wires. If I am wrong, I need to hear about it.

Thanks for help.
 

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I prefer not to add another relay and do extra wiring.

The referenced wiring chart (“12 Volt Wiring Gauge Requirements at specific Amps for Automotive Electrical Systems”) indicates that a ten-foot length of 18 AWG wire can safely (?) carry 15 amps at 12 volts. The size of the wire from the relay to the OEM horn is probably 18 AWG and measures between three and six feet, surely no longer than six. So, it should be able to handle up to a 15-amp draw with “normal” usage, that is, for short blasts – not laying on the horn button for minutes.

But using an “Automotive Wire Size Calculator” (http://www.gtsparkplugs.com/WireSizeCalc.html) I determined:
(a) 18 AWG wire no longer than 4.32 feet should be used to carry 10 amps at 13.8 volts (2% voltage drop).
(b) 18 AWG wire no longer than 2.88 feet should be used to carry 15 amps at 13.8 volts (2% voltage drop).

A tech representative at Wolo Horns told me that with “normal” usage each of the two horns draw about four amps, total of about 8 amps. Nevertheless, he said I should use a 15-amp fuse with the set of Wolo Maxi Sound horns. But if normal use draws 8 amps, I guess it would be OK to use the 10-amp fuse. If I stick with the OEM 10-amp fuse, will it decrease delivery of the full potential to the horns?

I want the full potential but I don’t want to burn up wires. If I am wrong, I need to hear about it.

Thanks for help.
10 amp fuse will not limit the horns. The fuse is designed to 'blow' if a draw of more than 10 amps occurs, which will keep the horns from operating. This is a safe guard to prevent burning the wires up.
 
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