Surging lights

The 2G was standard equipment and had an external fan and a 65 amp output.

The 3G upgrade was a modification that used a 130 amp alternator with an internal fan. It came from a 94-95 Mustang, and used a 4 gauge fused power lead and a 4 gauge engine to body ground. The 4 gauge power wire bolted to a 1/4" bolt on the back of the alternator.

Which alternator do you have?

See Stangnet 3G install sticky 3G Alternator Install: A How To - Mustang Forums at StangNet for more information on the 3G alternator installation.

Grounds are important to any electrical system, and especially to
computer controlled engines. In an automobile, the ground is
the return path for power to get back to the alternator and battery.

1.) The main power ground is from engine block to battery: it is
the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects.
The 3G has a 130 amp capacity, so you wire the power side
with 4 gauge wire. It stands to reason that the ground side
handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery & extra 3G
alternator ground wire as described above in paragraph 2. A screwdriver
points to the bolt that is the common ground point.
The battery common ground is a 10 gauge pigtail with the computer ground
attached to it.

Picture courtesy timewarped1972


Correct negative battery ground cable.

Have AutoZone or one of the auto parts chain stores check the alternator in the car. They will test it for free...