What baffles me is I did get them to work in series on my bench.
Well, that sort of shoots down my theory.
The diaphragm (finally spelled it right) on the low frequency horn would be moving in your series electrical arrangement, but not far enough to make a LOUD noise before the high frequency horn's switch interrupts the current flow.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
