On my Cuda, I eliminated the dimming and reduced firewall harness load by adding a bypass wire between the Alternator and Starter Relay stud and I added hidden relays under the battery to power all of the lights.

As it was pointed out, the power has to run through a crap-ton of connections before it ever gets to the lights so there is plenty of opportunity for voltage reduction.

Power leaves the Alternator then crosses through a bulkhead connection to get to weld at the ammeter. From there it goes to the light switch then into the foot dimmer then through another bulkhead harness to get to the lights. I think I left out a connection but you get the idea. Increasing the (idle) output of your Alternator with a different ALT one or smaller pulley will give you more power at low-RPMs but if your wiring system already has high resistance from older connections you will put further strain on those connections.

Relays near the lights will help you get their feed closer to the battery which helps but in my opinion it is not enough. Even if you connect the lights directly to the battery, the power still has come from the Alt which means you are sending the power through four firewall connectors and across the weld near the ammeter.

Installing relays and adding an Alternator bypass wire makes sure the load stays on the engine side of the firewall and takes considerable strain off the old connections in our cars.