On my ARP4 the dimmer potentiometer is fitted: It's in the wiring loom dangling loosely behind the lower rhs portion of the dash. It's just not installed in a way that you can easily reach it to adjust :-(

Ferrari 488 Pista
Porsche 991.2 GT3
Porsche 718 Spyder
Caterham 620R
BMW M2
Porsche Macan Turbo