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Finished the 90K5 Headlight Relay Modification

Discussion in 'The Garage' started by DPI, Jul 30, 2002.

  1. DPI

    DPI 1/2 ton status

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    This is a pretty straight forward mod. I replaced all wire from the relay to the lights, the ground wires, and the power wires with 10 guage fine strand. Here is the final wiring diagram for a 1990 K5. Not sure if prior years are the same, but years after should be. This mod really makes the factory headlights much brighter. This is due to connecting directly to the alternator or battery through the relays and not going through the high guage (low amperage) factory wire.

    [​IMG]
     
    Last edited: Jan 11, 2005
  2. MUDNUTT

    MUDNUTT 1/2 ton status

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    if i picked up some relays would this work on my 79?

    deck
     
  3. GRINCH

    GRINCH 1/2 ton status

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    Nice post... Steve should put this in the techie articles..

    Will be doing it also.
     
  4. DPI

    DPI 1/2 ton status

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    Yeah this should work for you, if you have 4 headlights. If you only have the two, just use the low beam portion of the diagram only. You will notice a big difference in brightness.
     
  5. DPI

    DPI 1/2 ton status

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    Thanks, If he wants to put it in the techie section, that would be OK with me. The hardest part of this was pulling out the old wires running under the radiator and re-running the 10 guage wires in their place. I wanted to install the new wires as "factory" as possible. Other than that is was a piece of cake.
     
  6. bigjbear

    bigjbear 1 ton status Staff Member Moderator

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    Cool, I was thinking about this after I installed a set of aux lights w/ a relay. Compared to others I had done w/o a relay set up they work better/brighter. Plus my headlight wiring has been hacked and spliced already.
     
  7. DPI

    DPI 1/2 ton status

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    I forgot to mention, the third relay closest to the bottom of the diagram keeps the low beams on while the high beams are on. This is basically the same set-up as the PainLessWiring mod.
     
  8. DPI

    DPI 1/2 ton status

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    Here is a pic of where I mounted the relays. Behind the aux. battery.

    [​IMG]
     
  9. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    What rating are the relays?
     
  10. Skigirl

    Skigirl 1/2 ton status

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    Wow! Great post! /forums/images/icons/cool.gif /forums/images/icons/cool.gif /forums/images/icons/cool.gif

    *Ski adds another mod to list* /forums/images/icons/smirk.gif
     
  11. DPI

    DPI 1/2 ton status

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    They are 30 Amp relays.
     
  12. HarryH3

    HarryH3 1 ton status Author

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    </font><blockquote><font class="small">In reply to:</font><hr />
    Yeah this should work for you, if you have 4 headlights. If you only have the two, just use the low beam portion of the diagram only.

    [/ QUOTE ]

    Actually, you still need 2 relays even with a 2 headlight system. Each lamp in the 2-light system has dual filaments, with a common ground. Connect the low-beam part of the circuit to the low beam filaments and the high beam part of the circuit to the high beam filaments. /forums/images/icons/cool.gif
     
  13. DPI

    DPI 1/2 ton status

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    Thanks for the clarification!
    dp
     
  14. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Okay, so I'll need the wire, the relays, 30 amp fuses? Can I get new connectors for the headlights from the parts store? Then wire everything from the lights into the alternator, then another wire to the battery? I'm thinking about doing this on my '87. Should be the same, right?
     
  15. HarryH3

    HarryH3 1 ton status Author

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    The only difference on an '87 will be if you have the over/under headlights. With that setup, all 4 lights are on in high beam mode. The upper lights have dual filaments. The high-beam wiring, right at the headlights, probably already has the high beam filament in the upper lights tied to the lower lights, which are high beam only. Just be sure that you keep them tied together so all of the high beams will be going through the relay. /forums/images/icons/cool.gif
     
  16. DPI

    DPI 1/2 ton status

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    Yeah, what Harry said. You can tie into your existing connector as close to the connector as you can, not sure if a parts store would have a new one, but the old one should work. The 89-91 K5s use a different style connector, it is basically a female splade. The wire from the alternator to the battery is not really necessary. The alternator should be feeding your lights. You should have an 8 guage wire already there. On mine, I did run another wire to the battery. I used a 4 guage. But I am running a dual battery setup and a winch and all that is charged through that 4 guage wire, so I wanted it large enough to handle the juice.
     
  17. 91GMCSuburban

    91GMCSuburban 1/2 ton status

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    worth reviewing
     
  18. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    Thanks DP 90K5! I was planning on doing this, just needed to figure out the wiring and you've don't it for me. SWEET! Of too the parts store for some 30 amp relays, wire and shrink tubing!!! What did the 30 amp relays cost you?
     
  19. DPI

    DPI 1/2 ton status

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    Man, I am surprised this is still around.

    I bought my relays and plugs here .

    They have excellent pricing and service!
     
  20. 91GMCSuburban

    91GMCSuburban 1/2 ton status

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    got part numbers?
     

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