One problem related to horn assembly has been reported for the 2005 Ford Mustang. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2005 Ford Mustang based on all problems reported for the 2005 Mustang.
I own a 2005 Ford Mustang gt rain leaks into the passenger side interior above the fuse and Smart junction box. When I was driving it in the rain I lost all electrical functions ie headlights,brake lights wipers, horn and so on. Luckily I was driving during the day and could see had it been night time I would have crashed. I called my Ford dealer and they stated that are aware of the water leaks with the Mustangs but did not offer to fix for a defect on their fault. A serarch of the internet shows many people with the same problem.