Head lites put a higher load on the system and may not show the flicker.
Flicker from the charge system under low loads is often the regulator going in and out of regulation. This raises and lower the voltage that low loads respond to more rapidly.
The other possability is a connection, ground etc independent of the charge system.
Monitor the voltage at low and high loads to get a lead on what might be a problem.
If the dash flickers and the system voltage does not move, then the dash feed has a problem.