alt light is randomly on

Ignition switch could cause the light to come on like this. When the light is off, 14.5 volts when light is on it is 12.8 volts. I have read blogs with people taking their Jaguar to the dealer. I have seen blogs with people paying up to $1200 for new alt. new battery and labor at dealer and still have same problem. I am still trying to find a definite yes the ecm could, could not guaranteed to cause this problem. If I hear it could it is the last thing other than ignition switch to replace.