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Quad Headlight Set up Assistance

Discussion in 'GM Electrical Tech' started by Goldie, Aug 29, 2010.

  1. Goldie

    Goldie Epic Member 5+ Years 1000 Posts

    My vehicle is a 2007 GMC W/T that I'd like to set up for the low beams to stay on when the hight beams are switched on. I have done quite a bit of searching of the the forums without a great deal of success. What I'm hoping someone can do is supply me with a simple step-by-step process, using just a relay, to accomplish this.
  2. clgoch187

    clgoch187 Rockstar 4 Years 500 Posts

    you could just spice the high beam power wire to the low beams with a diode in the middle so that the low beam signal doesnt back feed to the highs. only problem there is finding diodes.....not too many places sell em anymore, out dated tech i suppose .
  3. Goldie

    Goldie Epic Member 5+ Years 1000 Posts

    Thanks for the info. What size diode?
  4. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

  5. Mean_Green_95

    Mean_Green_95 Epic Member 5+ Years 1000 Posts

    You can get a relay kit from places like LMCtruck.com I used one of their kits, $20, on my 95 with absolute success. It comes with very detailed instructions too. I'm not sure if they have one for your truck, but you can get a relay and use the same methods I believe.
  6. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    I do not advocate the diode trick because you put too much load on the wiring and can cause fires. The factory wiring is only made to carry just the load of one set of lights. Doubling the load with a second set of lights can cause dangerous overheating, which leads to fires. Use relays where the load is switched onto heavier-gauge wiring.
  7. TritonBoulder47

    TritonBoulder47 Rockstar 4 Years 500 Posts

    That is why the diodes run between the trigger sides of the high beam and low beam relays... They don't run the full power through the diode...
  8. Goldie

    Goldie Epic Member 5+ Years 1000 Posts

    Thanks for all the help! My lows now stay on when the brights are activated. What I found out is that for my year and body style of truck is to run a 1n4004 diode between the #85 pin of the high beam relay and the #85 pin of the low beam relay, keeping the white stripe on the diode towards the high beam relay. For those of you interested, the relays are located in the under hood fuse block compartment. I tried using a relay with the same set up, but kept blowing the left low beam fuse.
    Thanks again for the help!
  9. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    Cool, I didn't realize that manufacturers stopped pulling the full power current through the headlight switch, though now that I think about it, it makes sense. Everything else is computerized now... Diodes on low-current trigger lines are absolutely fine. Cheers! :great:

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