Here is a link to a previous (2014) thread about the horns:
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1036816/1.html Steve H fron UT posted a link to the Truck Manual electrical listing which only lists one
capacitor in the truck electrical circuit. In answer to that Bill Flxible North of the 49th posted
that he’d never seen a capacitor in the horn circuit.
I posted back:
Bill if you take the horn apart, there is a flat paper wound condenser in there, it's part of the
LC circuit and determines what the circuit will resonate at. To small and the tone will be too
high, to large and it will be too low. Don't know what just right is but it shouldn't be too difficult
to try a few to see what sounds best, they're dirt cheap. But you are correct about the .2mf
cap listed, it's the one across the points in the distributor.DG.
Try starting out with something around 47 or .68 microfarad with a voltage rating of 250V.
Adjust the spring tension on the contact to get the circuit to resonate with the new cap.
Pix of the original cap:
http://www.pbase.com/dennygraham/image/155174087 Denny G
Also, if you want to pursue it further, here is an excellent paper describing the film capacitor
as applied to a Klaxon horn. Although it won't give you a specific value it should better explain
it's function in the internal circuit:
http://www.dekielectronics.com/pdf/deki-application-notes-film-capacitors-in-automotive-horns.pdf dg
