How-To: 4 High Headlight Mod For Free 99-02 GMT800.

[asilverblazer]

I have done this modification to my truck. Slightly different but same principle. It has been this way for quite some time now with no issues.

 

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[Dr. DanH]

Did this Mod to the Vette using 2 relays and 2 switches to get all 6 lights to work in any combination. Don't have a wiring diagram to translate this to trucks, but would really like to do this on the '07 'burb.

[ScottyBoy]

Ok I finally did the 4 headlight mod to my 01 Suburban. I did much testing of all the wires before cutting anything though, and heres what I found. I figured out why just grounding the yellow wires on the lowbeam bulbs works. Regardless of whether the truck is running or not, ign on, or off, or if the headlights are on or off, the yellow wires are grounded. They are always grounded until the highbeams are turned on, then they lose their ground. So rewiring the yellow to a constant 100% all the time ground ensure that the low beams will always come on, even when you turn on the high beams. The orange wire is hot when you switch on the headlights, and stays hot even when the highbeams are on. They go off when you turn on the highbeams cause they lose their ground, not the hot. This is why simply connecting the yellow to a ground works. I did mine under the relay center on the drivers side under the hood. I removed the entire cover(not just the access panel at the top). And the you can unclip the fuse/relay board and pull it up some to gain access to the bottom of it. Look for the wiring going to the headlight relay(in the lower left corner) and you should see the headlight wiring, it will be in a harness headed towards the front of the truck. You will see two yellow wire connected together on the same terminal. Cut these wires and tape off the side connected to the terminal on the fuse panel, the wires headed toward the headlights, tie the two together and ground them to a good ground. I used a 10mm bolt on the fender below the fuse panel. Now check your headlights, they should work as normal, but now when you turn on the highbeams, the lowbeams will stay on. If everything works, put thhe cover back on the fuse panel and close everything up, your now good to go. But let me stress that this ONLY WORKS ON 99-02 TRUCKS! 03 and newer have a dirrent circuit setup using seperate high and low relays.

[roberson104]

Ok I finally did the 4 headlight mod to my 01 Suburban. I did much testing of all the wires before cutting anything though, and heres what I found. I figured out why just grounding the yellow wires on the lowbeam bulbs works. Regardless of whether the truck is running or not, ign on, or off, or if the headlights are on or off, the yellow wires are grounded. They are always grounded until the highbeams are turned on, then they lose their ground. So rewiring the yellow to a constant 100% all the time ground ensure that the low beams will always come on, even when you turn on the high beams. The orange wire is hot when you switch on the headlights, and stays hot even when the highbeams are on. They go off when you turn on the highbeams cause they lose their ground, not the hot. This is why simply connecting the yellow to a ground works. I did mine under the relay center on the drivers side under the hood.  I removed the entire cover(not just the access panel at the top). And the you can unclip the fuse/relay board and pull it up some to gain access to the bottom of it. Look for the wiring going to the headlight relay(in the lower left corner) and you should see the headlight wiring, it will be in a harness headed towards the front of the truck. You will see two yellow wire connected together on the same terminal. Cut these wires and tape off the side connected to the terminal on the fuse panel, the wires headed toward the headlights, tie the two together and ground them to a good ground. I used a 10mm bolt on the fender below the fuse panel.  Now check your headlights, they should work as normal, but now when you turn on the highbeams, the lowbeams will stay on. If everything works, put thhe cover back on the fuse panel and close everything up, your now good to go.  But let me stress that this ONLY WORKS ON 99-02 TRUCKS! 03 and newer have a dirrent circuit setup using seperate high and low relays.

 

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Will the factory fog lights stay on too?

[ScottyBoy]

no, they wont stay on

[kssooner]

no, they wont stay on

 

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So from what I can see you pretty much did the same thing that 3500 in NC did it just in a different location. Im not very good at stuff like this so the easiest way to do it is the way for me.

[GMSea97]

Would this mod work for my 97? That easy?

[roberson104]

Ok I finally did the 4 headlight mod to my 01 Suburban. I did much testing of all the wires before cutting anything though, and heres what I found. I figured out why just grounding the yellow wires on the lowbeam bulbs works. Regardless of whether the truck is running or not, ign on, or off, or if the headlights are on or off, the yellow wires are grounded. They are always grounded until the highbeams are turned on, then they lose their ground. So rewiring the yellow to a constant 100% all the time ground ensure that the low beams will always come on, even when you turn on the high beams. The orange wire is hot when you switch on the headlights, and stays hot even when the highbeams are on. They go off when you turn on the highbeams cause they lose their ground, not the hot. This is why simply connecting the yellow to a ground works. I did mine under the relay center on the drivers side under the hood.  I removed the entire cover(not just the access panel at the top). And the you can unclip the fuse/relay board and pull it up some to gain access to the bottom of it. Look for the wiring going to the headlight relay(in the lower left corner) and you should see the headlight wiring, it will be in a harness headed towards the front of the truck. You will see two yellow wire connected together on the same terminal. Cut these wires and tape off the side connected to the terminal on the fuse panel, the wires headed toward the headlights, tie the two together and ground them to a good ground. I used a 10mm bolt on the fender below the fuse panel.  Now check your headlights, they should work as normal, but now when you turn on the highbeams, the lowbeams will stay on. If everything works, put thhe cover back on the fuse panel and close everything up, your now good to go.   But let me stress that this ONLY WORKS ON 99-02 TRUCKS! 03 and newer have a dirrent circuit setup using seperate high and low relays.

 

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Will the factory fog lights stay on too?

 

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[HyperBuzzin]

Would this mod work for my 97? That easy?

 

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If ya read towards the end, he did say.......

But let me stress that this ONLY WORKS ON 99-02 TRUCKS!

[ScottyBoy]

97's have green and tan headlight wires. Its a different setup. It can be done on a 97, but its not as simple as grounding a wire like on the 99-02 trucks. You can do it with a relay on the 97 trucks but I'm not 100%sure how to wire it up. I found these diections on a tech forum, maybe they will help.

 

 

88-98s

1. mount the relay on the inside fenderwell near battery

2. run a wire(green) from#87 to the low beam wire... you will need a test light

3. run a wire (Black) from #85 to a good ground with a self tapping screw or straight to the negative battery terminal

4 run a wire (white) from #86 to the high beam wire... test light helps.

5. last run a wire ( yellow) from#30 to the + side of the battery with an inline fuse.

6.tape up your connections and zip tie the wires... test it out first though..

[ScottyBoy]

no, they wont stay on

 

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So from what I can see you pretty much did the same thing that 3500 in NC did it just in a different location. Im not very good at stuff like this so the easiest way to do it is the way for me.

 

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Yes, you are right, I did basically the same thing, but not right behind the headlights, I did it under the fuse/relay panel. I did all my testing there, and then I decided to make my connections there as well for 2 reasons. One, I already had it all open, two I figure it would be less prone to water and weather under the protection of the fuse box cover. You can do it right behind the headlights and it will probably only take about 5 mins to do it that way being as how quick the lights pop out, but just make sure you wrap your wire connections VERY good in electric tape very tight to keep water out.

[larry derouin]

97's have green and tan headlight wires. Its a different setup. It can be done on a 97, but its not as simple as grounding a wire like on the 99-02 trucks. You can do it with a relay on the 97 trucks but I'm not 100%sure how to wire it up. I found these diections on a tech forum, maybe they will help.

 

 

88-98s

1. mount the relay on the inside fenderwell near battery

2. run a wire(green) from#87 to the low beam wire... you will need a test light

3. run a wire (Black) from #85 to a good ground with a self tapping screw or straight to the negative battery terminal

4 run a wire (white) from #86 to the high beam wire... test light helps.

5. last run a wire ( yellow) from#30 to the + side of the battery with an inline fuse.

6.tape up your connections and zip tie the wires... test it out first though..

 

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Did this with my 99 'burb (OBS) about 18 months ago. But used the kit from LMCTRUCK.com. No problems, and yes it will burn the retinas off a blind man with Silverstars or equivalent. Page 47 of the current catalog. Part # 36-3595. $19.95. Comes with Relay, Fuse, Wiring Harness, Instructions.

 

If you want a neat and clean install this is the way to go. However if you just can't wait, then the instructions will suffice. Use a 20amp fuse.

 

They also have a HEAVY DUTY HEADLIGHT HARNESS (for 90-98) that will power your headlights directly from the Battery, thru a relay. This way the Headlight switch isn't being loaded down from the lights and will run cooler and last longer. Part # 36-3580 (for Single sealed beam), and 36-3582 (for composite headlights). Either $29.95 Page 47.

 

Larry

[M J]

I actually, like to have control (control freak) -LOL

 

Someday im gunna figure a way to put a little switch on my column that activates all 4 (because i like the way the 2 and 2 look)

 

When you flash them...you look like a cop car at night ;) HAHAHAHA

 

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www.mrtaillight.com has this kit, at least for the 88-98 generation, so im sure they have it for the 99's. i bought it for my 1991.

 

 

there are sites out there that tell you how to disable DRL with techniques that have been tested over time with no problems, or sell like 5 dollar kits to do it, just to be safe

[Silverado25004x4]

This is NOT a very good way of doing it as you will be running all of the current for the Highs, lows and DRLs through the High's wires!!!

 

The Avalanche Forum guys have instructions on how to do it at the relay coils (under the fuse panel under the hood).  This way, the spliced wires are only handling the current for the low-current relay coils.  BTW, going this route, you'll need to wire in diodes.

 

Not sure if the same procedure will work for the Silverado, but that's the correct way to do it.

 

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thats not true, on the 99-00 trucks they are a switched ground, meaning that when the truck turns on, or lights in general, the lows and highs both get power, just the grounds for them are switched, so when you ground the low beams all it does is let them stay on with the highs when you turn them on. So really with the lows and highs both on its not gonna hurt anything at all, maybe a few deer or on-coming drivers but not the wiring.

 

As for the fogs, you can put a wire between the fog relay and the high beam relay, so when the highs are turned on they turn on the fogs as well.

[Corbin Dallas]

Take the headlights out of the truck then snip the yellow wires that come right out of the low beam bulbs, leave enough room to crimp a butt connector. then run the new wire to any available nearby bolt to ground the wire. it was super easy.:

 

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Call me what you would like, but which end of the yellow do we connect to ground? The one from the light, or the one back to the engine? What do we do with the other end? Or are we just adding a ground in-line to the yellow.

 

I know, give me a helmet before I hurt myself. Thanks.