There is a resistor on the three way switch. From what Mesa is telling me, the original horn was a celestion with a built in crossover. I had already ordered a current production horn. They are saying I need to get a current backplate.
I just acquired a Mesa diesel 2x10 cab. The horn has been removed. I've ordered a horn from Mesa there is a three way rocker switch for horn control- high off and low. Does anyone have a schematic on the correct wiring for the horn and switch?