electrical problem?

I have a 1999 mercury sable that has the strangest problem I've ever seen. When you push on he horn the check engine light comes on, the car slows down and as soon as you take you hand off the horn it surges forward. Also the theft light flashes at this time and by the way the horn does not honk. HELP!!!!!

You're gonna have to do some electrical troubleshooting with a mutimeter. There has got to be a short somewhere. Good luck

You are going to have to check the grounds too. Bad grounds can cause some strange sneaks.