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Wiring Tow Lights

Discussion in 'Early CJ5 and CJ6 Tech' started by colojeepguy, Aug 18, 2016.

  1. Aug 18, 2016
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

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    I've been flat towing my CJ for about 16 years with a set of magnetic towing lights, but after knocking one off and dragging it down the road the other day, I am thinking about wiring up the Jeep's taillights for towing. How do I go about that?
     
  2. Aug 18, 2016
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    Usually, you would splice into the wiring near the front of the Jeep that goes to the rear lights.
    Generally speaking, this could create a feedback thru the turn signal switch that would then make all of the lights flash.
    So, you would then install diodes in the wiring to the front lamps to stop the feedback.
    Or, you could wire a toggle switch, or simply unplug one of the front lamps when towing which should stop the feedback.
    This is all very easy to do and not as complicated as I have made it sound.
    I have a trailer female 4 wire plug mounted into my grille; I have a trailer plug harness that plugs into the female plug on tow vehicle to front of the female plug on the Jeep.
     
  3. Aug 18, 2016
    dnb5853

    dnb5853 Member 2019 Sponsor

    SLC, UT
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    Rig up a plug for your tail and brake lights (probably near the firewall). A 3 pole connection is all that's needed.
    Put a matching plug on your tow harness & bar. When you're ready to tow, unplug the vehicle harness and plug in the tow harness.This arrangement bypasses the turn signal switch and no diodes needed.
    That's what I do.
     
    Last edited: Aug 19, 2016
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  4. Aug 18, 2016
    Twin2

    Twin2 wasn't me 2020 Sponsor 2019 Sponsor

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  5. Aug 18, 2016
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    I did the trailer connector at the front and three toggle switches, one for the tail lights and one for each brake/turn signal.
     
  6. Aug 18, 2016
    termin8ed

    termin8ed I didn't do it Staff Member

    Mason, MI
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    I did the same thing. Made a harness with the flat 4 connectors and made it long enough to go from connector on tow vehicle to about the firewall. I wired flat 4 connectors to the brake and tail light wires under the heaterbox. Just unplug that and plug in harness to tow vehicle.
     
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  7. Aug 18, 2016
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
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    I did mine the same as above.
     
  8. Aug 18, 2016
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

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    I would really like to be able to just plug in and go, just like hooking up a trailer.
    I guess I need some sort of diode arrangement for that.
     
  9. Aug 18, 2016
    Framer Mike P

    Framer Mike P Member

    Hopkinton, NH
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    I have heard of people installing a second set of bulbs within the existing tail lights and then wiring them independently like a trailer with a connector up front.
     
  10. Aug 19, 2016
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    You can wire into the rear light wiring after the turn signal switch and wire in 3 diodes to eliminate the feedback issue. 1 diode for right turn, one for left turn, and one for tail lamps. This is what I do for many people and it works very well. No disconnecting needed, just plug into the installed plug of your choice. I prefer the flat 4 as it tends to have fewer corrosion issues than some other styles and they are small and easy to conceal.
     
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  11. Aug 19, 2016
    Tom_Hartz

    Tom_Hartz Member 2020 Sponsor 2019 Sponsor

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    This is how I did mine. Easy and it works great.
     
  12. Aug 19, 2016
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

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    Can you tell me what diodes you use?
     
  13. Aug 19, 2016
    timgr

    timgr Jeepin' Nerd 2020 Sponsor 2019 Sponsor

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    Picking a diode for this is straightforward.

    Something like an SB520 would work fine. http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/SB520/?qs=sGAEpiMZZMv%2bkWzvOmGqmozHG0J10gxF and http://www.fairchildsemi.com/ds/SB/SB560.pdf Pick a diode that has roughly double the voltage and amperage rating of your intended circuit. When you run the trailer lights, the diode is reverse biased, so that is where the voltage rating is relevant. When used by the Jeep, the current rating applies, which you can determine from the bulb wattage. P=IV, so a 5 watt watt bulb at 12 volts is 5/12 = 0.42 amps. Double that for your minimum current spec. Whatever Radio Shack has on a peg with minimum 20V and a couple amps rating will work fine - over-spec on these won't mater except to size and cost. (Cheap diodes will have a little more drop - see below).

    Note that the diode has a voltage drop and makes some heat, so I'd put it in the circuit where it was pretty close to the open air. The higher the current rating (and size), the less temperature increase there will be. Also, the voltage drop (here 0.55V) means that the bulbs in Jeep service will burn slightly less bright than without the diodes.The diodes have solid axial leads, and they will break if there is any bending of the harness. If I put them in them in the harness, I would use a cable clamp on the harness at that point to make sure they do not move.

    Also note that your trailer harness connects between the diode and the bulbs, and the band on the diodes is on the bulb (negative) side.

    Note also that the Jeep can still back-feed into the tow vehicle, so be sure to disconnect before you brake or light up the Jeep.
     
    Last edited: Aug 19, 2016
  14. Aug 19, 2016
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    For those of you who don't have self-cancelling turn signals you can simply move the signal lever up or down- this breaks the common connection between the stop lights & eliminates the diode requirement. One of your front lights will flash but that's not a biggie.

    H.
     
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  15. Aug 20, 2016
    william_cj3b

    william_cj3b 3BOB driver 2019 Sponsor

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    ^ This ^ Been doing it that way for 20 years! Only problem is when your turn signal switch is wired straight to battery vs. the accessory terminal on the ignition switch. In that case, just disconnect the battery and it will work.
     
  16. Aug 24, 2016
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    I think I would just get another set of magnetic tow lights.
     
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  17. Jul 19, 2018
    Focker

    Focker That's what I do, I know things and I fix stuff. Staff Member 2019 Sponsor

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    What was the outcome?
     
  18. Jul 20, 2018
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

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    No outcome...I'm still using the magnetic lights.
     
  19. Jul 20, 2018
    mickeykelley

    mickeykelley Well-Known Member

    Republic of Texas
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    I'm fixing to flat tow and had the same question, but the whole electrical engineering degree needed just to figure out diode thingy left me with 'I guess I'll go buy some magnetics'. Seems like it should be a simple go buy this part number xxxx diode and solder it in, but that's just me.
     
  20. Jul 20, 2018
    TIm E

    TIm E Member 2019 Sponsor

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