I had a '94 GMC, 1-ton, dualie, 4x4, diesel, etc, etc, that was a high option vehicle, and probably expensive when it was new. The headlights on it were terrible. I found out that there are aftermarket kits that run the wiring more directly to the battery, to get full voltage and brightness.
Evidently, GM ran the headlight wires through a gauntlet before getting them to the lights. The voltage drop was enough to make the lights dim. I'm gonna do what I can to get full battery voltage to the headlights for everything I build now.