I decided I wanted to put a big boy wolo horn in my 2010 honda fit. I cut the wire to the original horn hooked that to the positive of the big boy and then grounded it. It worked for a little while then stopped all of a sudden. I decided to just take everything off and try again another day when I went to put my car into gear it wouldn't move. I was able to use the shift bypass to make it home but I cannot seem to find the problem. The wire for the horn does have power when I use a multimeter, what could the problem be?

 

Maybe messing with the horn, since it's a big part of security, messed with the immobilizer?

 

I know exactly what you did because I've done exactly what you've done many a year ago.

Pull fuse #24 and you'll find it blown. This fuse controls your horn AND your brake lights, and by proxy the brake switch to let you get out of park. Replace this with another 10A. Now you need to wire a relay and battery tap to use that fused horn circuit as a ground to cycle the relay on or off. This will keep you from blowing fuses again (wolo pulls like 20-something amps on a circuit rated for 10A)

I can have a picture tomorrow of how mine is run if you need somewhere to start.