I've read about squirting WD-40 down inside the Mopar horns to revive them. What's the best process to get all the rust and etc. out of these horns please?

Thanks a lot!

For what it is worth WD40 is not a good penitrating oil. It is more of water displacer. That is what it was meant to be.
Us some PB Blaster or some Knockerloose.
Do they just make small noise or what. Have your tried to adjust it out of them buy turning on the tuner knob. It is the star shaped knob on them.

I knew that would come up but it is good stuff:

? are you trying to spray into the trumpet opening? The only thing that would do is possibly help dislodge dirt-etc.. The ""workings"" of the horn are sealed up inside the motor housing. There is a coil in there and a set of braker points. When the coil is enerjized the magnetic field draws a plunger (mobil nukleus) and that plunger opens the points and that drops out the "magnetic" field and repets.... as long as you hold the power to the horn. The "star wheel screw" adjusts the distance the points are from the "mobil nukleus". You should have continuity thru the horn. The "housing" is ground on most single terminal horns. ohms should be about 2to5 omhs.

screw in and out couple of times the tune screw to help to loose it and then tune up again.

In fact you can remove the screw, spray in through the hole some cleaner, shake it, drip the cleaner through the hole, fit the screw back and tune up.

Thanks!