So...this is a dumb question, or, maybe it's just im dumb, but how is the horn on a 1990 flh wired? Is it self-grounding, with the metal mounting bar on the horn? The horn i got to replace the cheesy aftermarket thing is pictured. The am horn has two wire terminals. The og has one terminal, but this one has a ground wire on that terminal. My wiring diagram isn't helpful here

 

Power to your horn is provided by a single wire, which you should find hiding under your gas tank, near where that bracket is bolted on, wondering when you will ever look for it! The ground connection is hiding at the top of your top photo, between the black bracket and the rubber mount. That doesn't look quite right to me, I have to add. I can't help thinking that ground strap, the funny wire woven thing, should go to the other side of the rubber mount. I have an aftermarket horn on mine, so it isn't much help to confirm what I just wrote!

 

I'm a little confused about what you've got there.

As grbrown says, it sure looks like the braided wire in the top picture is part of the ground connection.

Does it connect somehow to the bolt going through the rubber grommet/vibration isolator?

If so, then the bracket you're holding between your thumb and finger would also be part of the ground circuit for the horn.

And that would mean there has to be a second terminal somewhere on that horn for the wire that's bringing power from your horn button switch on the handlebar when you press the horn button.

Yet you say this horn has just that one terminal with the braided wire attached to it?

Is there another terminal hiding under the chrome cover somewhere?

 

If the horn pictured indeed has only one blade terminal on it then the horn is very probably grounded through the large PAL nut attaching the horn to the cad plated (silver colored) metal strap and the blade terminal on the horn is where the wire from the horn button attaches.
Not having the thing in hand myself and using the pictures you have posted, that's my thinking.

 

Just run one of your connections with a short lead under the bolt that holds the horn. Look to see if one is marked positive with a +.

 

They used to run a short ground strap from one side of the rubber mount to the other side of the rubber mount See #23

 

Yea...the spade terminal is for the power wire, and the horn grounds through the bracket. Realized it was the same wiring as some old automotive horns I'd nessed with, and gave it a shot. And it worked! So glad to have that over the cheesy aftermarket sqeaky thing

 

It seems like several horn configurations have been used.....one can adapt more or less....but they ain't all alike...some one wire, some two wire...and variety of brackets....