1999 Ford Mustang battery runs dead when sitting

My mustang has less than 35000 miles. When I do not drive it the battery runs dead. Usually it will only sit for a week or two when this happens. I bought it a year ago and it only had 4000 miles in it, it sat in a garage in Hawaii for 8 years. My experience with this issue is that it is usually the voltage regulator that causes this.I have owned a few older Mustangs but I am unfamiliar with this year, where do I find the voltage regulator on this model??