Voltage gauge drops to zero and then back up. It's iratic and not predictable. It stays off for awhile and then goes off. My edge box says good voltage and everything is working fine

Where might I start looking for a bad connection?

 

I noticed when I got home that I could see my parking lights and dash lights flicker some. Not terribly noticeable though. Plus as I watch my edge display the gauge seems to work when it says 13.7/13.8V. But I see it jump to 14.4V the truck gauge drops to 0. Maybe the alternator is going out and it's messing with the truck gauge

 

First, your instrument panel is can buss driven. Those gauges are receiver displays, not real gauges. I would assume that you have a flakey connection to the dash panel circuit board behind the dash, but hooking up a VOM to monitor system voltage is easy enough to verify.

 

Now I can turn my key on and the volt meter will say 12ish and then drop to zero (8) even before I start it.

But u checked alternator voltage at battery and I see 15-16v every once in a awhile. And now my check engine light is on

 

I'd also check the battery cables, and ground connection. Actually take them apart and make sure everything is bright and clean, and the wire strands aren't rotting.

As I understand it the system reads voltage from one battery and the alternator output is hooked to the other. If the parallel cables are flakey, it can give wonky voltage readings, and overcharge one battery.