I am new to 12V wiring and I am having trouble wiring up a dual trumpet Ongaro marine horn. Using my multi meter I am reading a solid 12V power source going into a push button switch from the ignition switch and a solid 12V power source coming out of the push button switch. If I wire only the first trumpet to the output of the switch the trumpet blows perfectly. If I wire only the second trumpet to the output of the switch the trumpet blows perfectly. If I wire both trumpets to the output of the switch both trumpets produce a barely audible humming sound. I have tried wiring serial and parallel with the same results.

I am hoping a 12V expert just read the above and is laughing at my obvious mistake!

Any suggestions would really be appreciated.

Thanks for the help,

Mark