98 R1100RT aftermarket horn-To relay or not to relay?, that is the question

I have read many of the aftermarket horn install threads and some say "I had to add a relay and a fuse'' and some say "they just used the existing wiring which already has the original relay and fuse". Which is correct?

I am installing a Stebel Nautilis compact air horn in my 98 R1100RT. I see in my Haynes manual wiring diagram that the bike already has a relay in place for the original horn.
Why would I need to use a different relay, fuse and wiring if all that already exists? I am confused.

Thanks for attemping to unconfuse me, and good luck!

Mark

Relay's are usually used in an electrical circuit to protect a switch.

I'll use an example of a radiator fan on a motorcycle. When the fan switches on it will draw somewhere around 5-10 amps. The temp sensor that tells the fan to come on is only designed to take a 1 amp draw. By wiring the relay into the circuit when the temp swtich closes it is only subject to the 1 amp draw but the way the relay works the fan will get its 5-10 amps. The relay itself is usually protected with a 30 amp fuse.

In the case of the horn when you press the horn button you are actually creating a dead short to ground that causes the horn to sound. If the current draw of the horn ( I don't know what it is ) but it is more than the small horn button can handle, therefore the relay in the circuit protects the horn button/switch from burning out.

If you can look at a automotive relay ( check online ) you'll see that there is about 5 contact points on the relay itself. These are all number & if you look at the accompaning drawing it will tell you what # goes where.

cycleman 2, Thanks for the info on the purpose of relays. I learn something here everyday. But it does not answer my question about having to add a new relay or can I rely on the original one that is already wired into the existing horn circuit?

Mark

Hi Mark:

Properly wired, the Stebel Nautilus draws 20A. The existing horn is fused at 15A.
Some people use the existing wiring and get away with it. The 15A fuse will hold more for short periods and the skinny wiring reduces current somewhat.

IMO for best results you need to wire the horn with the supplied relay directly to the battery(through 20A fuse) with heavy(at least 14AWG) wire. Then use the existing horn hot wire to power the new relay coil.

Yes, it's redundant, but it's easy and neat.

Motorrad Mike, Thank you, that is what I needed to know.

Mark

factory relay

I did nto use a different relay. I wired my air horns too the existing horn connection and it is doing very well.

Where did you mount the Stebel

Just bought one for my 1999 RT and Excel Werkes says it should fit without a problem in existing horn space. Looks like it will with plenty of clearance, thoughts or ideas?

You have a point Brewmeister, but regardless, the wimpy original horn is just plain embarrassing.

Mark