Why are the 2016 ford mustang heated seats not working?

While there are a number of reasons that the heated seats in Your 2016 Ford Mustang would fail to work, the most common is an issue with a damaged or shorted wire. The system therefore prevents electricity from flowing to the heating coils / packs, as this would represent a very obvious fire hazard. Ford has enough problems, they don't need burning Mustangs on their hands. It's also possible that the issue can be traced to a faulty switch or a failed heating element. The bad wire or a faulty switch will be relatively cheap and simple to replace, so if You're takeng the shotgun approach to fixing (replace parts until the problem is fixed), they're typically where You should start. Since the heating elements can be quite expensive, this is likely the last thing You'll want to swap out.