I have a 91 5.0 with a 3g upgrade.When I run the a/c,contour electric fans,and lights at night,the charging system is taking a beating to the point that my lights will flicker at idle.Anyone ever have this issue.
1.) Pull the alternator off the car and have it bench checked. All of the major auto parts chain stores will do it for free.
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 as much current, so it needs to be 4 gauge too.
The picture shows the common ground point for the battery , computer, & 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