I just am buttoning up a total headlight rewire on this car, I'll get some photos and details up tonight, what an adventure and wow did everyone suck at making cars in the late 80's early 90's?
Alright, I'll get pictures in a few minutes (or hours) but here's the gist of it....
1991 Capri XR2 (1.6, turbo, 5spd, kind of beat up), H4666 are stock headlamps, about as good as a D cell mag lite. Replaced with E-code H4 housings and a 12Ga wire harness that runs 4 relays, 4 fuses. Power comes from the battery via a 4 inch 10Ga feed to a 4 slot fuse block (marine grade) with 4 ATC 20A glow-blow fuses that feed out to 12Ga wire to 4 relays, one relay per filament per headlight controlled by the stock headlight circuit. Initial voltage drop from the factory 25 year old wiring was a total of 1.5 volts, new voltage drop is a total of .25 volts. The extra volt gains about 30% more light, the H4 vs H4666 gains about 30% more light, and being an ECE lighting pattern puts about 100% more light on the road where it's useful. Somehow to my naked eye that 60% gain is more like 100% on the garage door.