I have been having voltage gauge problems along with the battery light on.
I drive a 1989 F250 7.3 2wd
I have two new batteries, a brand new alternator, and brand new voltage regulator.

last week I drove it to work and it was fine. After my shift I turned the truck on the battery light came on. The voltage gauge was all the way over to the 8 (all the way to the left). The truck started just fine like always. At the time I had the old alternator in and knew it was going to die soon. So when I got home I did the alternator test and sure enough it was the alternator. I replaced the alternator and still the same thing. Then I figured it was the voltage regulator from past forums and replaced it. That helped some but the gauge is still fluctuating as I drive the truck, and the battery light is still on...

I have looked at the grounds and the terminals and cleaned the dirty ones and tightened them all back up.

I am stumped, I hope you guys can help me.

 

Just cause something is new don't mean it's good. Rip that alt out and take it to the parts store to be tested. While they're doing that, go over your regulator and control circuits and make sure that everything is as it should be.

Or...

Just do a 3G swap!