Highbeam/Fog lights mod done cheap!

Discussion in 'How-to Guides' started by Marcus, Nov 25, 2008.

  1. Marcus

    Marcus Rockstar

    So I recently purchased a '05 Silverado and noticed that when I turned on the high beams the low beams and fog lights would turn off. I started asking around seeing if this option could be overrode. After finding someone that knew how to do it they quoted me $50 bucks with parts and labor. After hearing that I began to do more research knowing that I could use that money for something else on my truck haha.

    My findings were this.

    Cost: -$1
    Tools: 7mm wrench, Needlenose pliers, 10mm socket and ratchet
    Skill level: Beginners

    Step 1:
    Go to your local radioshack and purchase a 12v diode. I used the part number 1N4004 but any 12v diode will work. They come in a two pack and that is all you need is two.

    Step 2:
    -Remove the two screws holding the dash peice under your steering wheel column. After removing those two screws you will have to remove the E-Brake release lever using the 10mm socket and ratchet. After removing all those clear the E-brake release lever out of the way.

    Step 3:
    -Remove the dash panel. It may take a little work but there are two prongs at the top of it that are pushed in and may take a little force to remove it. Before I did all this I removed the fuse panel cover just in case. Be extra careful when doing this because you may pull out the upper part of the dash by the 4x4 switch.

    Step 4:
    -Under the dash in the center you will see Three 24 pin plugs. The plug you are looking for is on the left side. The 24 pin plug is divided into two sectinos up and down with 12 pins on top of one another. The very first pin on the top row is your high beams (wire colors black and white, T1). The fourth pin from the left side is your Daytime Running lights (wire colors green and black, T4). The low beams are on the second row fourth pin from the left (wire color pink, B4) and your fog lights are to the right of that, fifth pin from the left (wire color green and white, B5).

    Step 5:
    -This is the hardest part of this trick. After locating all the pins you then have to decide what you want to do. Your order should go like this.

    If you want your high beams and low beams to stay on when the high beams are turned on connect the diode with the stripe facing the high beams to the low beams.

    T1----|==---- B4.

    If you want your fog lights to stay on with the highs and lows connect your other diode like this


    This allows are your lights to stay on with the high beams enganged.

    -The hardest part about this process is getting the diode to stick in the pin. I have found that removing the plug does not help any. It is actually easier to leave it in and push the diode in with a pair of needle nose pliers. It may take a few times but you can check your self by turning on the lights. I'm not sure what other vehicles this trick may work on but it should work for most GM's I would think.

    I hope this write up was helpful to you because the one I found was kind of confusing. If I failed to give certain pieces of information feel free to add or to give a better tip. Hope this helps!:happy:
    Last edited by a moderator: Nov 30, 2008
  2. retired2001

    retired2001 Epic Member 5+ Years 5000 Posts

    Sounds like a pretty straight forward operation. Thanks for sharing, I'm sure there will be a lot of "brighter" Chevies on the road after this! Thanks, again!
  3. ct9a

    ct9a Epic Member 5+ Years 1000 Posts

    Correct me if I'm wrong, but isn't this just for the NBS (I don't remember which years that was 03-06?). I think the procedure for the other years are different. I would edit that into the title for other users, or I can do it for you if you'd like.
  4. MWright936

    MWright936 Epic Member 5+ Years 1000 Posts

    I think I might try this after I get back from Thanksgiving vacation! I've wanted to do this, but didn't want to spend $50+ on a relay. I can afford a dollar, lol! Thanks for posting this!
  5. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    how big of a diode did you use? I'd say it needs to be at least a good 50 watt diode considering most headlight bulbs are about 55 watts a piece with aftermarket bulbs being 100 watts or so a piece.

    EDIT: Yeah, those look like 1 amp diodes. Unless GM and other car manufacturers have changed, all the current for the headlights flow through the switch. Therefore 1 amp diodes won't last for long and will potentially cause a fire. Keep that in mind.
    Last edited: Nov 26, 2008
  6. Marcus

    Marcus Rockstar

    this is how it was on NBS. It should would on other years but if the plugs do not look the same should not be to hard to get a test light and see which plugs you need to connect together. What size of diode would be more efficient then? I don't want my truck on fire lol.
  7. Springthing

    Springthing Epic Member 5+ Years 1000 Posts


    If the diode is still reachable after the dash has been put back together I suggest you do a little investigative reporting for us! Have a feel of the diode after having the lights on for some time to see if it's heated up at all. That would tell you how they're handling all the power and would let everyone know how the diodes hold up. It's one of those things, I think, that needs to be tried and checked. You seem to be in the perfect position for testing this out! :)
  8. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    I was thinking about what I said, and I have come to the conclusion that putting a diode in place is not safe in any case. Here's why...

    As previously stated, vehicles from the factory use the wires going through the light switch to power the headlights. Now, a vehicle manufacturer would not put an inssuficient sized wire in for the load, since that would not be up to code and could start fires. However, they put in wire that's just large enough to carry the load that they put on it from the factory. The diodes pass current from the high beam circuit to the low beam circuit, effectively doubling the load on the high beam wires. Since the wires were sized just large enough to power the factory high beams, 2 things can/will happen. First is that both the high and low beams will be dimmer than they would ordinarily be due to trying to cram twice the current down the same wire. Second, as a result of this increased load, the wire heats up from passing the current and can eventually melt the insulator and cause a fire.

    Now, the proper way to do it would be to utilize a pair of relays and a diode under the hood. You set the relays up so that the wire coming from the switch only switches the relay on which is pulling power through a new circuit coming straight from the battery( and is FUSED). Wire the diode in so that when the high beams are triggered, it passes power to the switch leg of the low beam relay. There are 3 advantages to this. One, when the lights are on by themselves, they will be slightly brighter than factory because they are no longer starving for power. Second, you achieve your goal of keeping the low beams on with the high. Third, all the wiring is now of proper sizing, and therfore stays COOL.

    I'd say that completing the project the correct way would cost in the neighborhood of 30 dollars (buying EVERYTHING from Radiorip) and about 2 hours of time.
  9. smainsw

    smainsw Rockstar

    Sounds like a good fix, however I work in the electrical field and the lights shouldn't be dimmer because you are trying to "cram twice the current" down the same wire, the current will go, your wire will get really hot and potentially cause a fire, but the current will go down the wire until it melts it more or less. And if your lights are dimmer it would be because there is a greater voltage drop across each of the lights wiring them that way then keeping them on their own circuit and doing the proper switching such as in your solution.

    I'm going to have to look into this I've been thinking about doing this to my truck for a little while, just haven't had the time.
  10. Springthing

    Springthing Epic Member 5+ Years 1000 Posts

    Faced with the same problem, I think I would just start from scratch...use the existing fog light switch, and run another circuit, complete with relay, to the fog lights so that it bypasses the system completely. It should be, what, about $20 worth of relay, fuse holder, and wire or so? Then you could turn the lights on and off at your leisure without anything to interfere.

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