You got me thinking there, so I just went out to the garage. When I turn on the parking lamps, motor running, the lighting in the lettering on the 3 big dials activates, not dims, as you said. On my truck, going down the road with the parking lamps off, the dial s are not illuminated, like the speedo, etc. The readout panel, where fan speed & temp is displayed is unaffected
with the parking lamps on.

I though, before actually trying it just now, that I had seen an actual improvement in daytime visiblity of A/C controls when running parking lamps. That is the case, at least on my truck.