I make reproduction Battery Horns for 1922-1927 Model T. The magneto horn started to appear on a few of the 1915 Model T but then was around for the entire production run through 1927 since the electric car with starter was an optional package. The electric car started in 1919 but the battery horn was not introduced until about March of 1922. Battery horn if adjusted properly should draw 5 amps DC and be fairly loud. The gap between the end of the plunger and the diaphragm should be set to 1/32" which is easy to set.. You just loosen the plunger lock nut and screw the plunger IN until a lite tap on the end of the plunger no longer delivers a "click" heard when it hits the diaphragm. Continue to screw the plunger IN to make it closer and eventually the click will go away because the plunger is touching it. Don't force this - you want the plunger to just barely contact the diaphragm and then back the plunger out 1 full turn since the thread on its plunger is a 10-32 thread and one turn = 1/32" advance or withdraw of the plunger. Once you have that spot then lock the locknut. Now fiddle with the point gap until you get 5 amps using 6V battery that is fully charged. Failure to achieve much sound or dim amounts can be a faulty horn winding or bad points but most often is because the diaphragm is full of rusted holes. I make new diaphragms out of stainless steel and use those on my horns but since all mechanical parts are made to factory drawings my diaphragm will fit your horn. Good luck with it
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