To back up this response, I use to be a diehard ford probe guy. I know that a lot of people had there probes engines messed up because the pullies took power away from the alternater, oil pump, and A/C. It's obvious why is might mess up the alternater, but with the oil pump not being powered as much, it supplies less oil to the cylinders...
For probes at least, it was create an oil starvation issue for cylinder 6, thus <i>screwing up the engine</i>. I dunno if it could be similar for mustangs but its probably something like that.