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Tech Mod
30,700 Posts
Discussion Starter #1 (Edited by Moderator)
Welcome to another of Beandip's How-To's

Today we are going to be upgrading the bread tie thin factory headlight wiring to something a little more beefy to increase the light output from your headlights.

There is already a How-To for this but it is for sealed beams, the same principle applies with this How-To but this one is for the 98+ trucks and has more pics.

I decided not to do a wiring diagram since the pics explain it themselves. This is a relatively simple mod but as stated in the other thread it does require some knowledge on what you are doing. The How-To was made after i upgraded my headlights so i tried to get as many pics of the process as i could without taking everything apart.

sealed beam How-To can be found here ---->http://www.s10forum.com/forum/f199/how-to-headlight-rewire-195221/

The How-To below shows upgrade for LOW BEAMS only.

Difficulty: Moderate

Equipment list:
30 Amp inline fuse
3M electrical tape
10 gauge black wire
10 gauge yellow wire
10 gauge quick connectors
10 gauge ring terminals
Wire cutter
Soldering Iron
4 SPDT 12v Bosch relays (http://www.partsexpress.com/pe/pshow...number=330-070)
Small flat screwdriver
Self tapping screws
Heat shrink tubing
DMM (Digital Multi-Meter....optional)

30 amp inline fuse not shown below

First step is to Disconnect the battery, after that remove the grille shell and headlights, then proceed to disconnect the connectors from the headlight and set the headlight aside.

Then start by getting the 10 gauge wiring and route it from the battery to the headlight area. There is a hole in the core support along with other wires that lead to the passenger side headlight (shown in following pics below). Do not connect power to it yet but loosely route it to determine how much wire you need.

OK, next lets start with the headlight plugs themselves. Shown below is the low beam plug.

To remove the connector inside, insert a paper clip here to release the clip holding the connector inside the headlight plug. Push down and you should feel it release, when it does gently pull the wire and the connector should come out.

I used an old codder pin but whatever works for you. Before you remove them mark a + and a - on the connector for future reference, blue is + yellow is -.

After you remove both connectors cut the wires as close as you can to the connector and SAVE THESE. Next you need to take both blue and yellow wires you just cut and feed them back though the wire loom to where the main harness connects. (explained later)

Now its time for soldering. Strip the end of the 10 gauge wire and insert it into the connectors you saved in the previous step.

Solder as shown here. The black wire should take place of the yellow factory negative wire and the red should be in place of the blue wire. Also the clip pointed in the pic needs to be brought out some so it can "click" back into the headlight connector after both wires have been soldered. If not then the connectors will pop out of the headlight connector when you try to plug them back in.

Re-insert the newly soldered plugs to the connector matching the + and - you wrote on the headlight plug. Give it a slight tug to ensure both connectors are seated securely inside the headlight plug.

Comparison pic of the wire thickness, low beam connector on the left, high beam on the right.

So now that you soldered both wires route them like this and cut the excess. The factory blue and yellow wires should be routed to where the relay is. Its a tight fit in the factory wire loom but just enough room to fit those 10 gauge wires.
From the general relay location route 1 red 10 gauge wire to the driver side headlight though the factory wire loom and rewire the low beam plug as you did with the passenger side one.

Wire the black 10 gauge wire from the headlight connector plug to this area here, this will be the ground for the passenger side headlight so ensure it is bare metal before you connect it (ignore 1 of the black wires, i made a mistake). Crimp and solder the wire to a ring terminal and tighten the bolt. On the driver side do the same, go from the headlight plug to the bolt on the driver side.

Also shown in the pic is where you route the constant 12 volts to the relay. MAKE SURE THE POWER WIRE IS IN WIRE LOOM TO PREVENT IT FROM SHORTING OUT!!!

OK now here is how you wire the relay, make sure before you bolt the relay to the core support that it will clear the headlight.

With the relay bolted on and wires hooked up.

After ensuring all the connections are secure and correct, install the connectors to the bulbs connect the main power wire and turn on the headlights. If you made a mistake somewhere the inline fuse will blow.

pic of the upgraded headlight wire

If the test is successful ensure the wires are in the wire loom and electrical tape the factory harness back to the way it was. Now install the headlights and grille shell, refer to this to make sure you installed your headlights correctly.http://www.s10forum.com/forum/f199/98-s10-head-light-install-how-to-171732/

Now my headlights are really shining and getting 14 volts to the bulb :cool:making my low beams brighter than my high beams. i rarely use the high beams so thats why i kept the factory wiring but i may upgrade them as well.

Quote from the sealed beam headlight rewire How-To
nismo said:
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 piss 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 piss 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, LMK.


If any of my pics do not work or have been deleted give me a PM and i will send them to you.


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