Having trouble replacing stock horns with FIAMM Low tone and High tone horns

I am replacing the stock horns with a pair of FIAMM Highway Blaster horns. I tried installing them according to the instructions, but one of the horns will not work and I have confirmed that the horn is not faulty.
One of the stock horn's factory connectors had two wires in it. The other horn's connector had just one. The FIAMM horns both have two male blade connectors.
I attached female blades to each of the wires from the dual-wire horn and connected those to one of the new horns.
I attached a female blade to the other wire, the single wire to the other stock horn, and connected that to one of the other new horn's terminals. A short wire with a female blade on one end and an eyelet on the other was provided, and that was to be connected to that horn's other terminal, and the eyelet was to be attached to the rear of that horn using the bolt that attaches the horn to the mounting bracket. See attached photo.
The problem is that only one horn; the one with the dual wires, works. I disconnected those dual wires and attached them to the other horn, but then neither worked. I left those attached and connected the single wire to the first horn, and neither worked.
So I only have one working horn; the one with the dual wires, and it only works if the other horn is connected to its wire.
What am I doing wrong? I appreciate the help! This is frustrating.

$19 FIAMM 72112 Freeway Blaster LOW Note Horn

https://www.amazon.com/dp/B000DINKPQ?ref=ppx_yo2ov_dt_b_product_details

$15 FIAMM 72102 Freeway Blaster HIGH Note Horn

https://www.amazon.com/dp/B000FKKOK6?ref=ppx_yo2ov_dt_b_product_details

 

It has to be grounded. Or your grounding it by mounting to metal and it’s not supposed to be?

 

I just put one on the sandrail had to mount it to plastic.

 

Are you referring to the horn with the single wire?
If so, I have connected that metal eyelet to the bolt that holds the horn to the chassis, as well as I have it pictured above. It doesn't work either way.