Electrical Question for Dim Headlights

[Johns 66]

Hello Peeps,

Got a question and not sure where to turn.

My headlights are dim, when I rev the motor they get brighter, at idle they go back dim.

I thought it may be a grounding issue so I changed the battery ground and added a better ground to the headlights.

so Im clueless at this point....

Im sure its an easy fix except Im not that knowledgeable about it.

I appreciate it,
John