FIAMM Horn Repair
Theory and Repair of Pantera FIAMM Horns
- Chuck Huber (Pantera Owner’s Club of Arizona)
I received a sweet, used pair of FIAMM horns, along with the stock mounting bracket, in a lot of parts I had purchased (see Figure 1). Unfortunately – the horns wouldn’t honk - neither one of them! So I resolved to look into this mystery…. Fast forward 4 years… I finally got tired of seeing the horns (disassembled) sitting on my shelf. So I decided to figure out how they worked, and to see if I could repair them. I tried pulling up YouTube videos of “FIAMM Horn Repair”, but these searches came up empty – I guess I would have to go it alone!
Figure 1 – Stock FIAMM High Note Horn
What I had found on initial disassembly was some surface rust on the diaphragm, and on the components within the horn body. My assumption was that the “points” within the horn were corroded and were not making contact.
The horns are actually a very simple electrical circuit. The FIAMM horns use a pair of electromagnets; these pull on a metal bar attached to the diaphragm. As the diaphragm deflects towards the magnets, a peg mounted to the metal bar opens up a set of points, cutting off the electrical current, and releasing the bar. When the diaphragm deflects far enough to its resting position, the points close, and the magnet comes on again. This happens very quickly. The key things to remember on this circuit:
· The initial (“resting”) position of the points is “CLOSED” (i.e. the circuit is a low resistance to ground)
· It is desirable that horn points should be adjusted so minimum deflection of the diaphragm is needed to open them
The challenge with the FIAMM horn is that the points are inaccessible to any tooling to allow you to polish the corrosion off the points. The solution is to drill out the two rivets that hold the point assembly to the body of the horn
Once the two rivets are drilled out, the point assembly can be completely disassembled, and the two sides of the points can be cleaned off with emery paper. Quick work with a small wire brush will knock off any stray corrosion on the rest of the parts. A powerful Shop-Vac will clean any debris out of the horn body.
Once the points are removed the wiring of the two electromagnets is very obvious (see Figure 4).
Reassembly was very straightforward. I used 8-32 stainless steel Allen-head cap screws, with close fitting washers on the inside and on the outside of the horn body. As there will certainly be a lot of vibration, I used both Loctite and nylon stop-nuts to retain the points. You can see the reassembled point assembly in Figure 5.
Adjustment is the next step. Carefully assemble the horns, ensuring the metal bar is aligned with each of the electromagnets. Using a multimeter, measure the resistance from the horn terminal to ground. Adjust the slotted screw on the outside of the horn body so that you are right at the point where your meter indicated continuity. You should be able to find the spot where a 1/4 turn of the external horn adjustment screw will close or open the points. Once you adjust the points to where they are just barely closed – get your wife’s nail polish and use it to mark the spot on the adjustment screw and to “stake” it in place.
For some reason – when I first reassembled my horns, I was unable to get the points to close… perhaps my gaskets had collapsed over the 45 years since the horns had last been used? Nevertheless – I was able to quickly correct this condition by cutting a slightly thicker gasket from cardboard - this gasket slightly moves the peg further away from the point assembly. This minor modification gave me the range of adjustment I needed to get continuity.
The final step is to test your horns with heavy gauge wire directly to the battery – remember that horns are one of the highest current drawing accessories in the vehicle. When doing your final installation on the car, ensure that you have high current capacity feeding the horns in your wiring harness through the use of a relay.
Figure 6 shows the final assembly of the two repaired horns on the stock Pantera bracket, ready for installation in your front passenger wheel well. Good Honking!
