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How To - Install Headlight Relays

Discussion in 'Early CJ-5 and CJ-6 Tech' started by Focker, Mar 15, 2017.

  1. Mar 15, 2017
    Focker

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

    Tri-Cities WA
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    This is for adding headlight relays only and keeping everything else stock. There's a bit of discussion from time to time regarding lighting upgrades. This is a cheap ($25-ish) and easy DIY for those who want to get full voltage to their existing headlights. I don't see any reason one couldn't upgrade to better bulbs/lights after doing this? I personally don't drive at night often enough to have worried about it, but after a little reading I see why the benefits outweigh doing nothing. At the minimum, it will protect the switch and the small stock gauge wires from overheating/failure (Yet...My Jeep's switch/wires are stock and 46 years old). Ok...I admit it...I just like doing stuff to my Jeep. :rolleyes:

    I was curious to see how much voltage was being lost through the Jeep's electrical system. I used a volt meter set to volts. I put the negative lead on the main chassis ground and the positive on the Jeep's lighting bus bar on the driver's side fender. All tests were performed with the Jeep off and just the headlights on.
    Battery reading - 12.73V

    Low beam = Black wire at bus bar.
    High beam = Red wire at buss bar.

    Before relays:
    Low beam = 10.70V
    High beam = 10.0V
    After:
    Low beam = 12.15V
    High beam = 11.85V

    Parts used...:lol:
    [​IMG]

    I had all this on hand, but here's a itemized list:
    1 - 4 Pin 30AMP 12V relay for Low Beam (you can use a 5 pin, exclude 87a).
    1 - 4 Pin 30AMP 12V relay for High Beam.
    8' - 10 gauge wire (Red power).
    8' - 10 gauge wire (Black ground).
    1 - 30AMP blade fuse/holder.
    Assorted spade connectors and splitters and miscellaneous 12 gauge wire for extensions.

    I found that the wires coming directly from the headlights were 12-14 gauge...So I kept them intact except for new spade connectors. I soldered all the connections with the exception of one female bullet connector, I crimped it.

    Disconnect your battery or battery disconnect switch.

    Here's the stock lighting bus bar...We're focused on the 2 far right lugs. They get their power directly from the headlight switch.

    Black (far right) is the Low Beam power source.
    Red is the High Beam power source.
    We're going to use and add length approx. 6" to these existing wires (later) to activate the each relay (pins 86).
    [​IMG]

    Remove the stock lighting block.

    Take the 2 light blue wires and strip one longer than the other. The yellow and blue wires with the brown plug will remain untouched as will the single black wire with black plug.
    [​IMG]

    Add a connector of your choice.
    [​IMG]

    Free up the harness routed to the passenger side headlight. Remove the stock wire rings and add the appropriate connectors. Black is low beam (LB relay pin 87) and red is high beam (HB relay pin 87). The female bullet connector goes to the male end already soldered in the previous pic. The 4th wire/plug remains untouched.
    [​IMG]

    Replace the wire rings on the driver's side with new connectors. Black is low beam (LB relay pin 87) and red is high beam (HB relay pin 87). Wait Focker...How are you going to connect 2 spade terminal connectors to one relay pin? That's coming.

    Space the relays far enough apart in order to use the existing holes that the stock lighting bus bar used. I'm using the left relay for LB and the right for HB. Connect a 10 gauge grounding wire jumped from pin 85 to 85 on each relay. Notice the dual spade connector I added? Add another dual spade connector to terminal 30 on the same relay. Make another short 10 gauge wire (red/pwr) jumping pins 30 on both relays.
    [​IMG]

    Plan your 30 AMP fused power...I went straight to the battery with 10 gauge wire and to the main chassis for ground. These wires run directly to the relays, pins 30 (power) and 85 (ground) on the HB relay. There's no particular reason I did this other than...That's how it ended up.
    [​IMG]

    Clean it up...I made a small bracket that this particular fuse holder had a groove for.
    [​IMG]

    Route the power and ground wires to the stock lighting bus bar location, mount the relays and connect it all. Once the relays were mounted I could determine how long the stock low beam and high beam extensions needed to be.

    High Beam Relay (DSC = Dual Spade Connectors)
    Pin 30 DSC = Power (red) from battery and jumped to LB relay.
    Pin 85 DSC = Ground (blk) from chassis ground and jumped to LB relay.
    Pin 86 = Stock HB source (red) stock wire extended 6".
    Pin 87 DSC = Stock HB wires (red) direct to headlights.

    Low Beam Relay (DSC = Dual Spade Connectors)
    Pin 30 = Power (red) jumped from HB relay.
    Pin 85 = Ground (blk) jumped from HB relay.
    Pin 86 = Stock LB source (blk) stock wire extended 6".
    Pin 87 DSC = Stock LB wires (blk) direct to headlights.

    The lower mounted relay is the Low Beam relay and the higher mounted relay is the High Beam.
    [​IMG]

    It's kind of jumbled, but I like it in the stock location. I'm personally not concerned about the exposed relay terminals. I added dialectic grease (not pictured).
    [​IMG]

    Passenger side cleaned up.
    [​IMG]
     
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  2. Mar 15, 2017
    Twin2

    Twin2 wasn't me Sponsor 2019 Sponsor

    Virginia Beach, VA
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    do headlight come on when you push start button ;);) daytime running lights
     
  3. Mar 15, 2017
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    Very good pictorial.
     
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  4. Mar 15, 2017
    Renegade ll

    Renegade ll Member

    Thayne Wyoming
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    Focker I just finished putting relays in for my high and low beams. When completed I checked for voltage drop and this is what I found. I also added fusable links that M.A.D. provided. I will try and add a picture or 2.

    Engine runnings 2000 RPM headlights on.
    At the the battery 14.5 V
    At the junction block 14.5 V
    At the headlights 14.2 V
    I would say it was a success.
     
    Last edited: Mar 15, 2017
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  5. Mar 15, 2017
    wheelie

    wheelie beeg dummy Sponsor 2019 Sponsor

    York, PA
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    Thanks F. This is great, especially for an electrically challenged person like myself. I've been wanting to do this for a while. Maybe I'll get to it one day soon.

    I know I keep asking but, is this suitable to be archived in the tech stuff?

    And, specifically, what relays did you use? Can I just pick up any old 30 amp relay.
     
  6. Mar 15, 2017
    Focker

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

    Tri-Cities WA
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    Hmmm... I just might have to look into that. :)
     
  7. Mar 15, 2017
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

    Medford Mass USA
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    The relays are a Bosch/Tyco style. You can get them from many places, but my favorite is Parts Express.
    "12 VDC Waterproof 5-Pin Bosch Style Relay SPDT 30/40A with Metal Bracket" from www.parts-express.com!
    They also sell a socket for these relays:
    "12 VDC 5-Pin Relay Socket For Bosch Type Relay" from www.parts-express.com!

    The main problem with the socket is the 14 ga wire, which is not as good as the 10 ga that Focker specs. If you choose to use 14 ga instead of 10 ga wire, the resistance of of 10' of 14 ga is 0.025 ohms, and 10' of 10 ga is 0.01 ohms, so a 0.015 ohm difference. This would be somewhat less than 1/2 volt at 30 amps, which is pretty much the worst case voltage drop. IMO the ground return through the body contributes the most to voltage drop, so I speculate that solely using 10 ga for the ground return direct to the battery will eliminate most of the voltage drop improvement the relay and new wiring provides.

    Aside from the reduction of voltage drop, the relay provides much higher capacity contacts than the switch provides. This is of most benefit when the headlight bulbs are upgraded so they draw more amps than the factory incandescent lights.

    I did this upgrade back in 1973, but I also installed Cibie' halogen headlights at the same time, which I heartily recommend. You can buy Auto Pal H4 lights on eBay for about $25, and at that price, anyone can try them out. If you want Hella or Cibie' they are considerably more.
     
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  8. Mar 15, 2017
    Focker

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

    Tri-Cities WA
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    Just your typical 4 pin 30AMP 12V relay from your local auto parts store. They're commonly in stock and hanging with all the electrical components.

    Edit - Tim's link is great if you want to save even more $. I usually stock up on stuff like this (as you can see from my junk drawer) so I have it on hand when inspiration strikes.
     
    Last edited: Mar 15, 2017
  9. Mar 15, 2017
    gunner

    gunner Member

    Washington state...
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    Did this on my A1 years ago. The military light switch is probably overkill for a simple system and even though it's 60+ years old, would probably still be fine. But I wanted to go with relays after reading up on it and coming to understand the advantages the relays give. I think I saw it on the MAD Electrical site. They specifically mentioned upgrading 60s-70s GM cars, which did not run relays. Any older vehicle can benefit from this upgrade. Newer cars have relays standard.

    I also used 10 gauge for the hot wire and took it off the post on the starter motor, where the positive battery cable ties in (the A1 has a floor starter which directly engages the starter- no firewall mounted solenoid needed). Ran that 10 ga wire to the relays. Also, I ran the ground wire all the way back to the pass side (the relays are behind the drivers side headlight) to the common ground lug I have for all the vehicle electrical grounds from firewall forward.

    Thanks for the effort, Focker
     
  10. Mar 15, 2017
    Daryl

    Daryl Sponsor Sponsor

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    You really only need one relay as you just put it in line between the headlight switch and the dimmer switch.
     
  11. Mar 15, 2017
    Focker

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

    Tri-Cities WA
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    What is this MAD site you guys speak of?
    I don't see the purpose of this? This negates the whole point of avoiding voltage drop through the switches, hot wires and possible switch failure.

    Besides... What's the fun in that? :D
     
  12. Mar 16, 2017
    Renegade ll

    Renegade ll Member

    Thayne Wyoming
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    M.A.D. Electric Catalog check it out. The tech tab has all kinds of neat stuff.
     
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  13. Mar 16, 2017
    timgr

    timgr Jeepin' Nerd Sponsor 2019 Sponsor

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    JMO - that defeats the purpose of adding relays. You still have the low capacity / low quality dimmer switch in the lights circuit, switching between your high and low beams. It also leaves most of the small diameter, lengthy and (thereby) high resistance factory wiring in place between the relay and the lights.

    The objective is to make a short and large gauge wire path between the battery and the lights. Putting the relays as close as possible to the lights reduces the amount of large-gauge wire needed.

    Nice write-up from Fokker.(y)
     
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  14. Mar 16, 2017
    william_cj3b

    william_cj3b 3BOB driver Sponsor 2019 Sponsor

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    Nice writeup! I did something similar to my F100 and Jeepster several years ago. Made a huge difference when running high wattage H4's.
     
  15. Mar 16, 2017
    piffey263

    piffey263 Active Member

    Sacramento, CA
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    You can easily take the prewired ends out of the housing and rewire to the correct guage you are using.Then reinsert to the housing. I did this on my truck, for the relay housing, and fuse block. This also elimantes the butt connector that would have been used.
     
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  16. Mar 17, 2017
    sterlclan

    sterlclan Member Sponsor

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    i did the same thing but used a third relay to run low and high at the same time.
     
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  17. Mar 19, 2017
    wheelie

    wheelie beeg dummy Sponsor 2019 Sponsor

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  18. Mar 19, 2017
    Focker

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

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    Sure you could. The only thing is the plugs for the headlights would have to be cut off or buy new headlights that take the plug.

    The way I did it was easy and I got to choose what gauge wires. It's hard to tell what gauge thier kit uses?
     
  19. Mar 19, 2017
    wheelie

    wheelie beeg dummy Sponsor 2019 Sponsor

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    Very true, the gauge of the wire,...and the quality of the wire.

    I thought all the plugs from that era, with round head lights, would be the same. The harness would be too long for the JEEP though so, I guess there would be a lot of cutting and re-soldering of the terminals and things.

    It was just a thought.:rolleyes:
     

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