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  1. #1

    Question Electrical Work.

    Ok, today I spent many hours working on the truck fixing some wiring I messed up. Well it is all good now, but I need some diodes to protect the system from backward feeding power. Does any one know what I should use?

    I'm protecting my back up light from back feeding in to the reverse circuit and the reverse lights. The light is a 55w utility light, that is activated either by the reverse circuit via a relay or by a switch on the dash. I need to make sure that when the switch is activated it doesn't back feed to the reverse circuit.

    Other work I did today was install new bulbs in the climate controlsClick image for larger version. 

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    1996 Chevy Tahoe LT 5.7L V8 4X4 205,000+ miles. Built proudly at Janesville Assembly in Janesville, Wisconsin
    Basic mods: Lights all over, bunch of electrical work, and a couple cooling mods.

    Check out my other mods in My Garage:

  2. #2
    Sr. Engineer
    Join Date
    Oct 2010
    Indianapolis, In


    If you go the relay route activated by the reverse/backup lights then no problems. If your back-up lights are activated by a switch on the transmision or the shift lever then you should have no problems with any back feeding issues when using a seperate switch. If activated by the body control module then maybe a blocking diode would be wise but not sure it would be neccessary. The only thing in my wiring diagram(99-06) is the automatic mirror adjust that would be activated by putting power to the back-up lamps.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  3. #3


    So you are saying I should not have a problem because the relay is protecting the reverse circuit.

  4. #4
    Jr. Engineer Jamm3r's Avatar
    Join Date
    Dec 2012
    Minneapolis area


    Yep. Unless you wired the switch to the relay coil, instead of in parallel with the contacts. In that case you need two relays. It's no big deal -- if you have a problem you'll see the reverse lights come on with the work lights when you use the switch, no damage done, just a nuisance problem.
    Minneapolis area - 1997 K2500 regular cab long bed + 8.5' Western Unimount plow + modified transmission + 2nd battery + modified camper charge circuit + 1971 Cayo camper -and- 2004 4x4 Suburban 2500 8.1 + Maxbrake controller + 2nd battery + modified trailer charge circuit + Reese receiver, pulls 30' Airstream trailer

  5. #5
    Jr. Engineer Jamm3r's Avatar
    Join Date
    Dec 2012
    Minneapolis area



    The relay should do the job for you if you have it wired correctly, no diode required.


  6. #6


    I have never heard of using diodes on American vehicles. On a MGB they are everywhere!

  7. #7


    That is because most american cars don't use many relays. I have used several relays in expanding my electrical system. In reality every car with an alternator has a diode.

  8. #8


    Yes, they are in the alternator. But as far as I know (and that's not much) no where else. But the English (as in Lucas Electric) They use them anywhere there's a back feed of juice.

  9. #9


    I've done the diode mod to my headlight relays such that my fogs and low beams stay on when my highs are on. I added 3 diodes to do this. I'll be adding one more diode when I do my rear work light install (which will be activated by either the reverse circuit or the cab switch I'll install). I might add another diode when I install my twin 10" LED light bars up front -- if I tie them to my high beams. (I'm undecided on that, yet, as it might be asking for trouble...)

  10. #10


    I will be doing the same diode set up as @SurrealOne for my back up light. I just need to buy the parts and find a warmer day for install. And learn to solder... I will also be doing the Lows one with Highs but my set up will be a little different because the OBS trucks don't have relays for each function of the headlights.

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