After making some new 3/8-16 BSW threaded rods to screw into the brass flags, I reinstalled my WT28 horns.
One of them sounded fine but the other sounded like it was blowing under water.
The way these work is an electo-magnet pulls up a diaphragm with a shaft on it, which pushes up the contact points, breaking the connection, and the diaphragm moves down again to repeat the cycle. The moving diaphragm moves air to make the hoot.
So here is how to adjust and fine tune the horns.
Use a points file to clean the contact points. My file is shown in the points.
There is a tiny hex screw with a locking nut that adjusts the gap between the plunger shaft and the points. My wrench is on the nut.
Mine had too small a gap and the diaphragm was not lifting high enough to make a good toot.
There was paint on the nut, indicating that nobody has touched it since Tuner No. 11 set it at the Lucas factory.
Probably the points were somewhat worn down, which changed the gap.