Keep in mind that with only the three wire self test horn #585992 available now keeping the diode would be the way to go. The horn will have to be replaced someday and that will create a problem somebody is going to have to figure out. IMHO
Before you do that you might want to check to see if you have a three wire horn? If it is a self test horn (when you turn the key on it sounds for just a second to show it works) then the blocking diode will have to be present or the motor will go into SLOW after each horn test after the ignition key is turned on. The diode is there to keep other horn functions from turning on SLOW. Only over heat is protected by SLOW. I believe only a three wire horn is availble for service now #585992. The horn has a purple, brown, and black lead. The momentary ground is what causes the horn to self test. A nice feature to prove the horn is operational at all times. Especially in salt water!
Dan in TN
PS, corrected my errors in previous post as of 9/1 early AM
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