kill switch in my 2003 stang is locking us out. put in new battery, still every so often will not let us start car
Aftermarket accessory: I'd remove it and replace it or just be done with it. If you're talking about the Anti-Theft feature from the Factory then you may have an issue with the chip in the key but the factory doesn't install a kill switch.
Search Ford Mustang Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Ford Mustang Experts