2004 Horn Honk from BW 4150

Do I need to use a relay for the (-) output from the brain to the (-) output to the horn wire coming from the steering colomn?

Yes, that way you won't burn out the output on the brain.Steve G

I hooked it up on the alarm without a relay and it works fine....is this bad?

It depends on how much the output can handle. Sometimes a good solid ground is needed to trigger the horn wire depending on the vehicle. I did a few horn outputs when I started installing and had problems with the internal relay getting stuck and having the horn sound constantly. I had to unplug the brain just to shut it up and add a relay. after that it worked fine. I had another time when i tried wiring the horn output directly and fried the horn output. I always use a relay now just to be on the safe side and for reliabilty. I would recommend using the relay but I can't say that it is absolutely neccessary.Steve G

Use the relay.  you'll be better off in the long run

Say the horn mysteriously stopped working today..blown output?

Quite possibly, test for a negative output when it should be sounding the horn.Steve G