[TonyB66]

This forum is awesome, once again.

theesotericone, the relay has: 87, 85, 30 and 86. Exactly as you depicted.

Even better, Mike, I won't need the relay? I think I saved an online version of the FSM, I believe on my work computer...

[TonyB66]

I did find this post:

Horn Relay Location

[theesotericone]

Originally Posted by TonyB66

This forum is awesome, once again.

theesotericone, the relay has: 87, 85, 30 and 86. Exactly as you depicted.

Even better, Mike, I won't need the relay? I think I saved an online version of the FSM, I believe on my work computer...

It depends on how you want the horn to sound. If you want a little louder than stock sound just hook them up to the existing factory horn wiring. If you want the real "GTF out of my way sound" you'll want to use the relay they came with. It doesn't matter if we have a factory horn relay. All your doing with the relay supplied with the horn is creating a circuit with to close a switch inside the relay that then allows more battery power to hit the horn. Read up on 12v relays and it'll become pretty clear what I'm trying to say.

[TonyB66]

Originally Posted by theesotericone

It depends on how you want the horn to sound. If you want a little louder than stock sound just hook them up to the existing factory horn wiring. If you want the real "GTF out of my way sound" you'll want to use the relay they came with. It doesn't matter if we have a factory horn relay. All your doing with the relay supplied with the horn is creating a circuit with to close a switch inside the relay that then allows more battery power to hit the horn. Read up on 12v relays and it'll become pretty clear what I'm trying to say.

"GTF out of my way" would be nice, and seems pretty straight-forward. I've installed relays before and understand what they do; but here, with there being a switch already in place, a relay being a switch, I'll need to look at this more to better understand why this addtional relay is beneficial.

Looks easy enough to do, and I'll try to find time tomorrow. Thanks again.

[octanejunkie]

From my experience, horns take power, like @theesotericone said, the more the louder! I agree 100% and would want to give a horn access to as much power as possible but not run that same [amperage] through a switch in the cab, hence the relay.

Looking at my FSM, and my truck, I cannot find a horn relay, which is odd - even my 59 pickup had a horn relay in the factory harness. I'm sure @TheDurk can advise. Running a relay behind a relay is somewhat inelegant and usually only creates an additional point of failure unless you are creating a conditional circuit. As far as the install, I found this https://www.youtube.com/watch?v=50KrBMlQryE he's a chatty cathy

Looking at the FIAMM 74100 El Grande horn, it does not come with a relay (according to "what's in the package") and others here have installed these horns in a "plug and play" capacity - but I would be interested to hear how they sound with and without the additional relay. Regarding the swap, I found this https://www.youtube.com/watch?v=rSz-pNrp69g I'm not impressed but home recordings often leave a lot to be desired.

IMO It's easy enough to mock up a relay with wire nuts and tape, do it both way, find out and report back

[4Runner4Leon]

There is no Horn Relay in the 3rd Gens, the power is supplied directly by the Body ECU once the horn switch (horn button) is closed:



The real question as to whether to use a relay is not related to voltage, but to amp draw. If your new horns draw more amps than the factory horns do, then you might need to add a relay and larger wiring to provide the needed amps. If the amp draw is similar, then you don't need the relay.

The only way the horn would sound louder with a relay (and larger wiring, because a relay itself is just a switch) is if there was a significant voltage drop across the current wires. Otherwise, they are both 12V and will sound the same as long as they get 12V.

One way to check amp draw is to measure the resistance of factory horns and new horns. If resistance is similar, so is the amp draw. If the new horns have lower resistance, then they will have a higher amp draw (I = V/R) and you might want to add the relay and larger wires.

[TonyB66]

Thanks much for the input everyone. Dang busy day with work, wife's b-day, so I'll reply more later.

Both factory horns off, each reads about 2.8 to 2.9 Ohms (measuring over the course of about 20-30 seconds)

The replacements, each measures 1.9 to 2 Ohms

So...

Factory horns draw about 4.2 amps (12/2.85).

Replacement horns draw about 6.2 amps (12/1.95).

Replacements draw about 50% more power. Seems worthwhile to do the relay.

The horn wires are about 10" apart and need to be on that relay together of course. Would prefer that to be in a well-protected place in the engine bay. I guess I can add extensions onto each horn wire, or better yet, find their location further up... This might have been much easier when the radiator was out.

[octanejunkie]

Just run one wire back from the + of one of the horn cables to the relay and then make a new horn wire harness that goes back out to the new horns and zip tie it to the core support using the holes along the top (guess who else did that when they ran wires across the core support without pulling the radiator) you can pretty it up later. Wire is cheap. IIRC you bough a spool of speaker wire you can borrow from.

Happy birthday Tony's wife

[4Runner4Leon]

Originally Posted by TonyB66

Thanks much for the input everyone. Dang busy day with work, wife's b-day, so I'll reply more later.

Both factory horns off, each reads about 2.8 to 2.9 Ohms (measuring over the course of about 20-30 seconds)

The replacements, each measures 1.9 to 2 Ohms

So...

Factory horns draw about 4.2 amps (12/2.85).

Replacement horns draw about 6.2 amps (12/1.95).

Replacements draw about 50% more power. Seems worthwhile to do the relay.

The horn wires are about 10" apart and need to be on that relay together of course. Would prefer that to be in a well-protected place in the engine bay. I guess I can add extensions onto each horn wire, or better yet, find their location further up... This might have been much easier when the radiator was out.

I bet it's fine as is, but if you want to be extra sure, then move the + wire feeding the horns to the switching terminal of the relay, then run a larger wire from battery or fuse block to the switched relay terminals and then to the new horns.

Sent from my SM-G900P using Tapatalk

[TonyB66]

Originally Posted by octanejunkie

Just run one wire back from the + of one of the horn cables to the relay and then make a new horn wire harness that goes back out to the new horns and zip tie it to the core support using the holes along the top (guess who else did that when they ran wires across the core support without pulling the radiator) you can pretty it up later. Wire is cheap. IIRC you bough a spool of speaker wire you can borrow from.

Happy birthday Tony's wife

Thanks Mike. Not sure she'd approve of me on the forum now, lol.

The factory horns are one wire. So, I'll run the passenger side horn wire back to the vicinity the driver side horn and try to find a good place for the relay there (side of radiator, near headlight).

So, that 14 gauge speaker wire is fine here?

[octanejunkie]

14ga speaker wire is more than fine, it's golden

[TonyB66]

Originally Posted by octanejunkie

14ga speaker wire is more than fine, it's golden

Hoping it won't be too thick for routing purposes. Should have time today to tackle this... Will likely use solder and heatshrink tubing on the extension/s.

For power, straight from the battery or is there somewhere else to consider, like maybe an open fuse, or use an Add-a-Circuit, which i have a couple?

[4Runner4Leon]

Originally Posted by TonyB66

Hoping it won't be too thick for routing purposes. Should have time today to tackle this... Will likely use solder and heatshrink tubing on the extension/s.

For power, straight from the battery or is there somewhere else to consider, like maybe an open fuse, or use an Add-a-Circuit, which i have a couple?

I'd use an open fuse or add-a-circuit, it's more elegant. If you do go straight from battery or other unfused terminal, be sure to add an inline fuse.

Like I said before, I think this is largely overkill - your new horn is not that high power a device, and it is not continuous duty like headlights (unless you lay on the horn nonstop ), so it won't have time to heat up and reduce ampacity of wires (which is what wires are all sized for). I still think your existing circuit/wiring would have been perfectly adequate. But I realize we tend to do a lot of overkill on our trucks, that's part of the fun .

[TonyB66]

Originally Posted by 4Runner4Leon

I'd use an open fuse or add-a-circuit, it's more elegant. If you do go straight from battery or other unfused terminal, be sure to add an inline fuse.

Like I said before, I think this is largely overkill - your new horn is not that high power a device, and it is not continuous duty like headlights (unless you lay on the horn nonstop ), so it won't have time to heat up and reduce ampacity of wires (which is what wires are all sized for). I still think your existing circuit/wiring would have been perfectly adequate. But I realize we tend to do a lot of overkill on our trucks, that's part of the fun .

You got me thinking again... Maybe I can use a sound meter here. I've done that before on exhaust system testing. That was an actual SPL though, and I don't know where that is now... Have an app though, that seems quite sensitive. I can measure stock first, then these replacement horns with no relay, then those horns with a relay.

[4Runner4Leon]

Originally Posted by TonyB66

You got me thinking again... Maybe I can use a sound meter here. I've done that before on exhaust system testing. That was an actual SPL though, and I don't know where that is now... Have an app though, that seems quite sensitive. I can measure stock first, then these replacement horns with no relay, then those horns with a relay.

Easiest thing to do is first try the new horns with your current wiring (no relay), then hook them up directly to a battery with some heavy cables (e.g. booster cables) and try that. My expectation is that you'll see (hear) zero difference in sound.