Looking for some troubleshooting help here. With engine running and RPM at appx 3500-3800 my headlights and dash lights dim. Also, the volt gauge goes from 14v down to 8v or 9v. Anyone ever have this issue or have any thoughts on what it might be? Thanks

 

Possible serpentine belt slipping due to a weak belt tensioner and/or a glazed belt. I have also seen alternators with a faulty rectifier cause similar issues. The only way to spot it is on an ocilloscope.