1994 Bonneville erratic charging

Hi all, I am new to this site and it seems helpful. I have a 1994 Bonneville with charging problems. When started the gage on the dash might go up to 14 and stay there or not charge at all. The car at times while driving will charge then not charge and then charge again it is all over the place. I have put on a new battery, Alt. and starter still the same thing. I have had the car at Battery Specialist and they said its in the wiring...I have put a new harness on and still the same thing...What the hell???,What am I not seeing? Any help would be great.:crying:

With a voltmeter across the battery, is the voltage constant while the car is running, and is the reading on the dash erratic?

Which harness did you replace?

If a scan tool is reading the same as the voltmeter, it looks like a cluster problem, or a connection problem at the cluster...

If the volt gage on the dash is showing low charge the car drains the battery, if the gage shows normal charge then everything is fine...can the cluster cause this?... You can actually hear when the car is charging and when it quits......The alt. battery and starter are new but sometimes you get a faulty part so I had them checked and all are good...I replaced the main harness from the firewall that includes the injectors and alt. connecters.