The Stovebolt Site Forums The Shop Area The Electrical Bay Art Deco gauge lights

My '45 gauge lights seem to do a funny thing. They are bright when the park lights are on , but when the headlights go on, they dim noticeably. I am still on the 6 volt system. I use a headlight relay. The dimmer switch is clean, grounded and works well. The headlight switch is original. The wiring harness is a modern type.
The question is, is this dimming a designed in feature, or an electrical issue?

you don't remember the very old Disney cartoons showing old cars whose radio lamp dims when people talked
same thing here

my 6v 356 does the same