I have not seen anything mentioned so far about a headlight modification to make either your low beams and or both your fog lights &low beamswork while your high beams are on. So check this one out. My buddy found it while surfing the web.
Enjoy: I will be doing mine shortly... could be a few hours or a few days.

http://www.performancetrucks.net/for...ge=1&pp=10

 

sweet way around buying a kit which is alot more expensive...awesome find, thanks!

 

thanks man,that is some usefull imformation.Do you know if that will work on a 02 silverado?

 

im sure it will...theyre the same lights arent they?

 

No! I think the 02 and below is a different setup. You need to read on. There is 15 pages of information. Read carefully. And as the starter of the thread besure to turn of the ignition and seperate the plug before starting. No need to F something up with a shocking charge of 12 volts.

 

lol yeah true that even if it is different...they steps probably follows the same general order

 

i did this under the hood with the relays. you just use three you need adn the number 85 on them.

 

Well I did the Diode trick under my steering column finally like the Thread said and got all my lights: High/ Low/ and the Fog lights to all light up when I turn on my high Beams. What a difference.
Has anyone tried grounding the Yellow wire behind the head light on a 99 to 2002 model yet?

 

Have you done the mod on your truck yet?

 

The 99-02 setup is different. There is a yellow wire under the grid in your underhood fuse box that you need to run to a ground...
Go to fullsizechevy forums and search "4 hi mod"...