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I know it is Friday, but please don't dog pile.....
Just to be clear:
1) If I order the PIAA 85114, do I get two horns or one?
The 85114 is a kit with two slimline horns. One 400Hz horn and one 500Hz horn.
2) Can I replace one FJR horn and keep the other stock?
Yes, I did. I replaced just the right hand (higher tone) horn with a single PIAA 500Hz slimline horn. PIAA part number 76501
3) Can I replace the crappy horn on my KLR with the PIAA horn?
Yup. You sure can. Just use one of the same 500Hz horns as above
Also, the reason to replace just one horn is that you get the same benefit at half the price. The stock higher tone horn is very high frequency, around 2000 Hz as I recall, which is what makes it sound like the road runner cartoon instead of like a car horn.