So last year, I installed a flash to pass (garage door opener), which connects to the high beam circuit. When I peeled back the insulation to solder the wires to it, I was shocked at how thin the wire was. It was maybe 8 thin strands of copper, possibly 22 or 24 gauge. Not a lot of meat in there at all.
So today, before I did the mod, I measured the voltage at the light bulb (by fishing very thin krynar wire to connector and pinching it between bulb and connector) with the engine running.
Battery: 14.42 volts.
low beam at the bulb: 12.48 volts.
high beam at the bulb: 12.73 volts.
I then installed the relay harness. Amazon.com: Putco 239008HW Premium Automotive Lighting Wiring H13-9008 100W Heavy Duty Harness and Relay: Automotive
It is an easy install, and if it took over an hour, you're doing it wrong. On the passenger side I picked up the ground near the headlight, and on the driver side I picked it up below the airbox where there is another ground. It is all plug and play, I did have to extend the ground on the passenger side. The harness features a direct line to the battery for each circuit (low and high), and a pair of fuseable links that connect to the battery. Very well made with 14 gauge (guess) wire, and a pair of 30 amp relays.
After the install, I got these numbers:
Low Beam: 14.14
Significantly better! I have not had darkness yet, but even comparing one to the other half way through the install, with one connected to the harness and the other OEM, it seemed obvious that the relay side was brighter.
Here is a voltage vs lumens from Danial Stern:
10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens ←Rated output voltage
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens ←Rated life voltage
14.5V : 1528 lumens Daniel Stern Lighting Consultancy and Supply
So, according to this, I gained about ~350 lumens per side, a fairly significant number.
Bulb life may be cut a bit, we shall see. On my old car, I used a diode to bridge between the high beam --> to low beam circuit, but that was with a 9004 bulb. IIRC, it blew up. Envelope temp got exceeded. But for those willing to risk it......the option is there.
The other option is to get higher intensity bulbs, but I have not even begun to look for those. With the harness in place, this is an easy option to exercise.
I wish the harness had black sheathing instead of the crazy yellow, but since I don't do the car show thing, no biggy.