I have an 89 mustang lx 5.0 and I am having low voltage problems. I have replaced the stock alternator 3 times and tried 3 different batteries and the voltage at idle rarely passes 11.8 give or take a tenth. This causes the car battery to lose all voltage and the car shuts off and needs to be jump started. once its jumped, it will run alright until i shut it off again or it dies, and then it will need another jump start. Any input?? I just ordered a 140 amp alternator to see if that helps and i will be buying a new bigger battery as well. I can give more details about the accessories I am running if need be.