Audi A6 C6 cluster fuel gauge and unstable idle after changing alternator

[Talbert]

Cluster is no longer coming on,fuel gauge is no longer working and the idle is unstable.I once had the alternator problem and dealer put a cheap regulator so when it happens a few days ago I decided to buy a new Valeo alternator.the voltage I'm getting on the battery is 14.1.Can anyone help me out please 

[Steve Q]

My advice would be a diagnostic check.