Battery Wont Charge 1984 Mustang V8 5.0

You showing any codes?

Get out your DVM or multimeter because you are going to get to do some
voltage checks.
The voltage regulator has 3 wires according to the above diagram.
1.) The black/orange wire is the alternator power feed to the car and
should always have 12 volts or more
2.) The yellow/white wire is the power feed to the regulator and should always
have 12 volts or more
3.) Lt green/red wire is the switched power to the regulator and will have 12
volts or more any time the ignition switch is in the Run position.
4.) The White/black wire coming from the voltage regulator will have a variable voltage
on it any time the ignition switch is in the Run position. As the battery gets closer to full
charge, this voltage will decrease. I would expect that with a low battery, this wire would
have the full battery voltage on it.
5.) Notice the two fusible links – you should see 12 volts or more on both sides of
the link. If you find 12 volts on one side but not the other, the fusible link has burned open.

The one thing that I do not understand about this diagram is the connection between the
white/black wire on the alternator to the choke heater. It may be a sneaky way to turn the
choke heater off as the engine warms up. However, I would use the DVM or multimeter to
confirm resistance between the white/black wire going to it and ground. I would expect
to see less than 100 ohms here.

FYI:
AutoZone wiring diagrams

http://www.autozone.com/servlet/UiB..._us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model Mustangs

http://www.autozone.com/servlet/UiB..._us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model Mustangs

http://www.autozone.com/servlet/UiB..._us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp for 94-98 model Mustangs