Henry, I recently worked on the horns on my '54 Champion. You're right,
there is not much on the net on repairing horns. I have messed with a
number of horns, and they are not really difficult to get working
again.

IMHO, I wouldn't take the horn apart yet. I'm also not sure blasting
the coil and associated parts would be worthwhile, unless they are
really rusty......in which case you may want to find a horn in better
shape. If you do blast them, use a 'gentle' abrasive media.

First, knock the horn body on a piece of wood or knock the body with a
rubber mallet to break loose any debris (or mud dauber nests in my
area<G>) inside, and shake it out. Horns work by moving a diaphragm and
this movement of the diaphragm moves air inside the curled body and
makes the horn sound. (All of you horn techies, I know this is a very
un-technical explanation, but we don't necessarily need to know all the
detailed physics on how the horn works to do this repair<G>!) The coil
(electromagnet) on the horn is mounted around a 'stem' attached to the
middle of the diaphragm, and this coil pulling on the stem is what
makes the diaphragm move. There is a set of contacts (basically a set
of points) on the top of the coil that make and break the current,
which causes the coil to move the diaphragm up and down. Normally,
aside from wire problems, these contacts get dirty, burned, and out of
adjustment and the horn doesn't blow. So, we'll concentrate on these
contacts first.

Take the sheetmetal cover off the top if you haven't already. Clean the
whole top of the horn (coil, contacts, etc) off with an electrical
spray cleaner, and blow it off good with compressed air. Repair any bad
or frayed wires. If the wire itself is in good condition, but the cloth
cover is frayed, you can put shrink wrap over it, or use some of the
'liquid electrical tape (made by PlastiDip, the same company that makes
the liquid rubber like you use for coating plier handles, etc) or both.

Get some crocus cloth (not emery paper!) and WD-40 and clean the
contacts really good. Clean the WD-40 off with a good contact cleaner.
Hook the wires up, and see if the horn blows. If not, or if it is weak,
loosen the lock nut on the adjuster and adjust until you have a good
tone, and then lock the nut back down. Replace the sheetmetal cover,
and you're done!

This will take care of 90+ percent of most horn problems. If it still
doesn't work, it may have worse problems like a cracked diaphragm, the
stem broken off the diaphragm, coil windings bad, etc. Normally there
is nothing that goes wrong inside, AFAIK, unless something stops up the
passageway. If you did take the body apart, I suppose you can use some
small stainless nuts/bolts or similar to put it back together. I think
there is also some sort of gasket between the halves, but I have never
had to take one of these apart so I am not positive.

Disclaimer: The above is my experience, and I don't claim to know much
about them 'thar horns except what I have related.<G>

Paul