Do I need a relay for installing aftermarket horns?

[Paul De]

I purchased a high and low tone pair of Fiamm Freeway Blaster horns (models F-72112 & E-72102). They are electric and not air horns. I'm thinking I would install them in parallel and in that configuration the current draw will be more than what the stock horn draws. So, do I need to add a relay circuit on my '99 R1100RT, or is the stock wiring circuit robust enough to handle an occasional blast?

[Edgar]

I installed Fiam horns (2) and did not add a relay. I installed one in the original horn position and the second in the right speaker bracket. It works fine. I wired them in from the original wiring and added a hot leg for the one in the bracket from the original location. The horn grounds itself from the bracket. It is a marked improvement over the factory horn.

[Vincent]

Paul, possibly! I added 1 Fiamm highway blaster along with my stock horn, no problems after 5 years. If you remove the stock horn, and run both blasters you should not have a problem. There have been some post in the past that people adding Fiamms blew fuses. I would try it first without a relay. Good riding!

[RFW]

Just put the relay in there and be done with it. They cost almost nothing. Why would you even bother to spend time worrying about it!

 

Bob.

[John in VA]

FWIW, I found a used pair of R1150RT horns to replace my stock R1100RT horn. I just used the existing wiring/relay with no problem, but I don't know if they draw any more juice than your Fiamms.

[JonathanE]

Yes, you certainly do need a relay.

 

With that new relay, comes the major reason for installing it, bigger wire. While you may not melt your stock wire with occasional horn use, the two new horns will be starved for voltage due to the resistance of the wimpy stock wire.

 

I've tested wire sizes for horn circuits. I recommend either doubling up #12 AWG wire, or do what I did and pull a #10 AWG circuit.

 

It will make a huge difference in the performance of your new horns. It's likely that the new horns won't actually operate if they are added to the original stock horn circuit.

[SAAB93driver]

I installed dual Fiamm disc horns without adding another relay, no problems.

[RFW]

Yes, you certainly do need a relay.

 

With that new relay, comes the major reason for installing it, bigger wire. While you may not melt your stock wire with occasional horn use, the two new horns will be starved for voltage due to the resistance of the wimpy stock wire.

 

I've tested wire sizes for horn circuits. I recommend either doubling up #12 AWG wire, or do what I did and pull a #10 AWG circuit.

I agree that you need to probably upgrade the minimal stock wire size, but using #12 (or TWO parallal strands of #12) is getting a bit absurd.

 

Six feet of #12 wire (3 feet each way) will result in a voltage drop of a mere 0.09 Volts, assuming the horns draw a constant 10 Amps. That's less than a tenth of a volt! Doubling up with 2 parallel strands of #12 will result in a voltage loss of 0.045 Volts. Now THAT is clearly a case of "diminishing returns". Hell, the bike's voltage varies more than that when riding!

 

If the voltage drop is kept to less than a quarter of a volt, the slight reduction in horn volume will be insignificant, and you won't need a pipe bender to bend the wire when installing it

 

AWG14 or AWG16 wire is a lot easier to work with, and (again assuming the horns draw 10 Amps, and there is a 6 foot total run of wire), the voltage loss will only be 0.15 Volts, or 0.24 Volts (respectively). As I said, a mere quarter of a volt will not make a noticeable difference in horn volume.

 

But DO use a relay! It is not just because of the voltage drop incurred with the bike's wiring. The bike's horn switch was never meant to carry this level of current, and you run the risk of eventually frying its contacts if you don't.

 

Bob.

[Pilgrim]

Yes, you certainly do need a relay.

 

But DO use a relay! It is not just because of the voltage drop incurred with the bike's wiring. The bike's horn switch was never meant to carry this level of current, and you run the risk of eventually frying its contacts if you don't.

Bob.

 

I wondered if someone would get around to that. Wire is only the issue in small part. The horn gets such little use (by most of us, anyway)that it would take a long time to ruin the switch, but each press of the button will result in some slight erosion of the contacts. The process accelerates as the degradation proceeds.

 

Use the relay.

 

Pilgrim

 

Pilgrim

[Davis]

Adding a relay/larger wires to increase the voltage getting to your new horns is a benefit

 

Adding a relay to reduce the wear on the horn switch is silly, there is already a relay for the stock horn and the switch on the handlebar is only switching the relay's coil current with or without an additional relay/larger wire.

[flyingreg]

Adding a relay to reduce the wear on the horn switch is silly, there is already a relay for the stock horn and the switch on the handlebar is only switching the relay's coil current with or without an additional relay/larger wire.

I was wondering about this subject, but kept quiet because I have an 1150, not a 1100, and didn't know if the 1100 had a relay.

 

I have slightly the same question and posted it on another thread, but maybe this is where my question should be laid before you all.

 

I recently installed a pair of Magnum Blaster Horns, both Hi & Lo tone (138 decibels!!). Very easy install on the 1150RT, bolted right up to stock brackets. The horns work great, will definitely wake the most inattentive driver self consumed with the morning paper or cell phone use. I highly recommend these, THEY ARE LOUD BEYOND BELIEF!

 

The horns called for a 10A fuse. I switched the stock 7.5A fuse for a 10A fuse.

 

My question is, will the stock wiring handle the additional 2.5A current load without overheating? 2.5A doesn't sound like much, but don't wish to have to hunt down a burned wire that has melted to ground when I am somewhere in the middle of nowhere.

 

Does anyone know the wire size used between the relay and horns on the 1100 or 1150?

[Davis]

I don't have my wiring diagram or bike handy but IIRC the stock horn wiring is 1.0mm or about 18AWG and I assume PVC insulation (worse case anyway) In free air this is rated for about 15A. Even when installed as wires in a protective tube or installation conduit (which is closer to the conditions on the motorcycle) it is rated for 10.4A. If it was the headlight or a constant use circuit, I'd upgrade the wire. But it's a horn, how long do you use it 1-2 sec?

 

The voltage at your new horns is only about .2V less at 10A than it was at 7.5A, so if you're horns work and sound good to you I wouldn't worry about the wiring. On the other hand, your 10A load is getting close to the rated capacity of the wiring, so if you use the horn a lot and for long periods then maybe you should upgrade the wiring.

[Paul De]

Great input folks. I needed to ask the question because my dear sweet wife had "organized" the books in the den and it has taken two days to find my Haynes manual!! Got my manual located now and here is what I found out

 

The wiring diagram shows that the R1100 has a horn relay protecting the horn switch and that the entire horn circuit is protected with a 15 amp fuse. I found on the Web that my horns draw 5 amps each. I will install the horns without adding a second relay and line. I'll let you all know how it works out

[SAAB93driver]

procedure to fit dual fiamms given here

 

http://www.ibmwr.org/r-tech/oilheads/R11dual-horns.shtml

 

As stated there is already a relay for the horn. If one wants to fit relays, do it for the headlight. There you can make useful a difference.

[Pilgrim]

Right. Shame on me. I didn't think there was one, and I didn't look at the wiring diagram.

 

But make sure that you do use the existing relay.

 

Pilgrim

 

 

Adding a relay/larger wires to increase the voltage getting to your new horns is a benefit

 

Adding a relay to reduce the wear on the horn switch is silly, there is already a relay for the stock horn and the switch on the handlebar is only switching the relay's coil current with or without an additional relay/larger wire.