The alternator is new and the battery is only a year old but shows full charge. I have added nothing when I noticed the pulsing. I have replaced the windshield wiper motor, the door lock actuators and new headlight bulbs, the pulsing still remains the same.

 

OK all, I have a bit more information for you. The wife and I took the Mustang out for a little drive tonight and we discovered something new with the pulsing. SHe was getting cold so we turned on the heater (which didn't work) but she turned the blower on high and teh pulsing stopped. As we lowered the blower speed, the pulsing increased. It does it with both the heater and the AC. The charge indicator, with the blower at on the highest setting, would drop below the halfway point on the 8 volt side. When the blower is low or off, the needle jumps up above halfway on the 18 volt side and jumps with the pulsing. Hopefully this info can help. Thanks