New horn install issue

[Bminder]

So I got a loud Wolo Horn from J&P to replace the Wimpy Wimpy Wimpy horn the bike came with.
Before i removed the old horn, turned the key on, engine off, and hit the horn button and it just kind of warbled, not it's usual 'beep'. I started the bike and revved it and the old horn worked fine.
Installed the new horn. When the motor off, turned the key on and hit the horn button and only heard a little click down there.
Started the bike, revved it up and the new horn worked fine.
But when it's idling, it won't beep. Only above 1500 rpms or so will it work.
What's going on?

[Rhino]

did you instal it with a relay and new wiring from the battery?

[Bminder]

No I just used the same connections from the old horn. It plugged right in.

[RichBaker]

You need to install the relay with the power to the horn wired direct from the batt to the relay, use the original horn wire to control the relay.....

[Bminder]

What kind of relay? I've never installed one. Why would the old horn work without one and the new one need one?

[RichBaker]

The Wolo should have had one with it. They're necessary because the compressor draws quite a bit more current, and the various connections in the horn circuit cause voltage drops, which reduces the voltage available to the horn, due to resistance in the connection. This is also the reason the horn doesn't work well at idle, the lower voltage means even less current available to drive the horn...
If it didn't come with a relay, most auto parts stores carry replacement relays.
Any of these would work...

[Bminder]

It doesn't have a compressor it's the old fashioned automotive type.

[Arnie]

Its still drawing more power than the old horn.
If you're unlucky, you'll blow the 'signals' fuse too.

Arnie

[jamesearthdrum]

Its still drawing more power than the old horn.
If you're unlucky, you'll blow the 'signals' fuse too.

Arnie

and if you have an '89, the signal fuse is also the fuel pump circuit!!

[RichBaker]

OK, I was thinking of this one. It doesn't come with a relay, either, but should.  I bought a Stebel Nautilus a couple years ago, it DID come with a relay....

[Arnie]

Somewhere on the horn there should be an info plate that will list the power required.
It will say, 12V and #.#A.  The A stands for Amps.  The stock FJ horn draws 2.5A IIRC.
Amazon do not list the A for this horn, but the Nautilus which is similar (and claimed louder) draws 18A.

Arnie 

[ribbert]

Lots of people complain of premature failure with these horns. They dry up. I've had that same horn on my bike for 3 or 4 years and it died several times early on. Lubricating it fixed it.
I now take it off once a year, remove the horn and oil it (through the inlet) while spinning it over with a battery on the bench, hold a rag over the outlet.
Still works as good as the day I put it on.
Noel