This applies for the sealed beams, but may apply to the later headlights as well.
Please be careful when doing this modification. This is not complicated, but it does take some understanding of what you're doing, as well as some ability to solder.
3M electrical tape
10 gauge black wire (from Autozone or the like)
10 gauge yellow(from Autozone)
12 - 10 gauge Butt connectors
12 - 10 gauge ring terminals (yellow color)
Double relay sockets from Parts Express (http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=330-078)
4 SPDT (single pole, double throw) 12v Bosch relays (http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=330-070)
Plastic split loom 1/2"-3/4"
Assorted zip ties
Drill with 1/4" or so drill bit
Small flat screwdriver
Here's the wiring colors:
Brown is high beam
Green is low beam
Blue is ground
Brown is high beam
Green is low beam
Black is ground
The wires that go to the headlights start right in front of the ABS pump. The bundle of wires contains the power wire for ABS, headlight wires, horn wires. There is just enough room to sneak 2 10 gauge traces from the battery in there.
In order to install the relays, removal of the battery/battery tray, airbox and wiper fluid box would make life MUCH easier. Also, remove the grill, and all the clips that hold the split loom (they open by prying with a screwdriver and are reusable).
It's easiest to start on the passenger side, but you can start on the drivers side if you want. Remove the grounds from next to the radiator, and remove the horn wiring (one clip in the fender), and also remove the wire from the headlight. Pull the split loom out so you can work with it easier. Peel the electrical tape from the loom so you can get at all the connections.
You can put the relays wherever you want, but I chose to put mine inside the grill, between the headlight and the radiator.
Here's a good time to get the relay harnesses ready for wiring. The harnesses come with one white trigger and two grounds (can be wired as one white ground and 2 black triggers...this is what we will do). First of all, take the small screwdriver and stick it in the end of the harness (where the relay sits), and push the retaining tabs in on the blue and red connections. If you've done this right, then they will pop out...and you should have 4 wires laying out in front of you. Pick one red one and one blue one. The center of the relay harness will be left empty, but you will put one red and one blue each in the open outside hole. In order for them to stay in, you must bend the retaining clips back out on the terminals. They aren't very large, but you'll see them on the smooth side of the terminal and you'll want to angle them at about 45 degrees. At this point, the harness should have a red wire for one relay and a blue wire for the other one. This is so that you can remember later which is your high beam and which is your low beam. Repeat for the other relay harness.
Take the screwdriver and pop out the headlight terminals just like you did with the relay harness (and leave the other headlight harness together for reference ). Once you've popped out the harness, you need to cut off 6" or so from the terminal end. SAVE THESE!!!!!! One by one, you'll want to take the terminals and solder them to the red and blue wires from the relay harness. I suggest brown being wired to blue and green to red so that your blues are high beams (up to you though). Bend the retainer clip back out on the healight terminals, and reinsert them where they go. At this point, you'll want to run the ground for the headlight. It will come straight out of the headlight connector, and go to where the stock ground is (on the radiator surround just like the stock wires). I would try to keep the ground less than 1 foot.
Now, take the wires that come from the headlight switch and wire the black (blue on drivers side) to the white connector on the relay harness. Take the brown headlight wire, and solder or butt connect it to the black wire from the BLUE wired relay. Take the green headlight wire and solder or butt connect it to the black wire from the RED wired relay. Repeat for drivers side headlight.
As of now, you have not wired up power for the headlights, though the headlights are wired to the harnesses. Take the yellow 10 gauge wire and make one run to each relay harness from the battery position, by running the wire inside the split loom to both sides. On the connection from the battery wire to the relays, its easiest to use butt connectors because soldering wire that large doesn't work well.
Some will say put a fuse holder between the battery and the headlights, but the relays will blow if there's a problem, and the fuses are extra stuff to blow and leave you without headlights...so I didn't use fuses on mine. Actually, I have my batteries in the bed, so I don't even have the battery in the way. I had a spare 1 Farad Streetwires capacitor that I installed next to the horn, and ran 1/0 wire from the alternator and ground to the cap. This is extreme overkill, done only because I don't have a place under the hood to jump start my truck or someone elses vehicle and because that's all I had laying around.
I think I got everything. If you have a question, comment, or positive results, please feel free to share in this thread or PM me.
If you have a DMM, it would be in your interest to check the voltage on the headlights before and after the relay mod so you know how much difference there is. I had 2.0 volts of drop, now I have 0.2 volts drop from the battery voltage and now my lows are brighter than my highs before. I'm also getting just a SLIGHT blue color at the edges of my headlights -- damn near HID baby!
Some of you have been contacting me to ask why I did this, and if it will do anything for you. Well, the reason I made the HOW-TO, was because of how poor the lighting on our trucks is. There are 2 problems with the headlights on our trucks. The pattern is so terrible, it would need to improve to be poor, and the wiring that feeds them power is so thin I wouldn't suggest using it for anything but a twist tie.
Now the HOW-TO only fixes half the problems. It improves output greatly by upping the voltage at the bulb. For every 10% drop in voltage, you lose nearly 45% of your lighting iirc. I don't know what your headlights are getting, but mine were sitting @ 12.5v with the truck voltage at 14.2v. That is roughly a 12% drop in voltage, and roughly 50% of your light bulbs output.
Now, you CAN put in a brighter bulb...that draws more amperage. Unfortunately, you compound the problem by doing that. The more amperage you pull though a given wire, the MORE voltage drop you get. You need to take the restriction off the poor factory wiring, and feed the bulbs with a more solid current flow.
By doing this wiring, my low beams are better now than my high beams were. Soon, I hope to replace the headlamp housing with an E-code (European code) headlamp. That will allow me to have a better pattern, plus I can use an H4 bulb instead of having to replace the entire housing every time, and I can use better bulbs too.
I think I've probably said too much, but if you have any other questions, let me know.