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  •  » Help: Adding Relays to Headlights

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    12/05/2022 8:07 AM  #1

    TremendousWand
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    Registered: 5/16/2013
    Posts: 657

    Help: Adding Relays to Headlights

    1966 Mustang Coupe, 5.0 Swap, EFI, T5z, Painless Wiring harness

    I'm trying to add 2 relays to my headlights in order to fix my headlights blinking when they are on for too long.  
    I bought 2 4-pin relays from amazon.

    Image 1 is the wiring harness diagram from painelss wiring which I installed few years back.  It shows two wires coming from the dimmer switch and one wire going to the headlight switch:
    https://ibb.co/6BDF9cJ

    Here's the diagram I found showing how to wire relays for the stock wiring diagram:
    https://ibb.co/gVgF5Ps

    As you can see, it shows the need for 2 relays, one for low and one for the high beam.  


    Here's the relays I ordered:
    https://ibb.co/41FTDL9
    https://ibb.co/JBTQH8r
    https://ibb.co/LxNxH4X
    https://ibb.co/PjfxQgG

    These colors seem odd.  I know that the 30 wire is the fused power that goes directly to the battery source but that's about all I can figure out.  Based on the diagram, I think the 30 would be the blue wire for some reason.  Can someone help break this down?  Which color corresponds to which pin?  Based on the wiring diagrams how should I wire this?  Is a headlight relay normally off with a ground or positive trigger.  

    Thank you


     

    Last edited by TremendousWand (12/05/2022 8:37 AM)

     

    12/05/2022 8:55 AM  #2

    TKOPerformance
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    From: Newark, DE
    Registered: 12/15/2014
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    Re: Help: Adding Relays to Headlights

    You are over complicating it.  The pin assignments on the relays are all that matters.  30 goes to battery + (or starter solenoid is often easier to tie into by just using a ring terminal), 85 to chassis ground, 86 to the +wire coming from the headlight switch for the high or low beam depending on which the relay is being used for, and 87 to the headlight plug + for either high or low depending on which element the relay is used for. 

     

    12/05/2022 10:51 AM  #3

    TremendousWand
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    Re: Help: Adding Relays to Headlights

    TKOPerformance wrote:

    You are over complicating it.  The pin assignments on the relays are all that matters.  30 goes to battery + (or starter solenoid is often easier to tie into by just using a ring terminal), 85 to chassis ground, 86 to the +wire coming from the headlight switch for the high or low beam depending on which the relay is being used for, and 87 to the headlight plug + for either high or low depending on which element the relay is used for. 

    So which wire is which pin?  It seems dumb but the color scheme is throwing me off.  I'm fairly certain that the blue wire is the 30 pin.  So then the black wire is the ground (85) and then the 86 and 87 correspond to the white and red. Is this correct?  Does getting the 86 and 87 pin backwards mess anything up?

       •Thread Starter
     

    12/05/2022 11:34 AM  #4

    Bullet Bob
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    From: Montrose, Colorado
    Registered: 4/01/2013
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    Re: Help: Adding Relays to Headlights

    Well, I looked at the pix of the relays you have and it appears to me that the black and white wire are smaller gauge than the red/blue.  If that's the case this is what I'd do, unless you have an ohm meter to ring the silly thing out.
    Black wire to ground.  White wire to the low beam or high beam wire from the  dimmer switch.  Red wire to the battery (starter solenoid) THROUGH A 20 AMP FUSE! Blue wire to either the high or low beam wire from the head lights.  You cut the wires from the dimmer to the headlights and interpose the relay in each circuit.   If you have an ohm meter we can prove all of this easily.  Failing that, call back and I'll walk you through testing with a couple of jumpers and a light bulb.

    BB1
     

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    12/05/2022 11:39 AM  #5

    Bullet Bob
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    Re: Help: Adding Relays to Headlights

    TremendousWand wrote:

    TKOPerformance wrote:

    You are over complicating it.  The pin assignments on the relays are all that matters.  30 goes to battery + (or starter solenoid is often easier to tie into by just using a ring terminal), 85 to chassis ground, 86 to the +wire coming from the headlight switch for the high or low beam depending on which the relay is being used for, and 87 to the headlight plug + for either high or low depending on which element the relay is used for. 

    So which wire is which pin?  It seems dumb but the color scheme is throwing me off.  I'm fairly certain that the blue wire is the 30 pin.  So then the black wire is the ground (85) and then the 86 and 87 correspond to the white and red. Is this correct?  Does getting the 86 and 87 pin backwards mess anything up?

    Yes!  86 and 85 are the pins to the relay operating coil.  87 is the normally open contact that 30 connects to when the relay is switched.  85 and 86 are not critical as long as one goes to the dimmer and one goes to ground.  Same with 30 and 87 though normally power will be delivered to 30 and sent out 87 but that's also not really critical in this application.

     

    Last edited by Bullet Bob (12/05/2022 11:40 AM)

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    12/05/2022 12:44 PM  #6

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: Help: Adding Relays to Headlights

    I believe I have a diagram for this on the TIPS forum

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    12/05/2022 3:27 PM  #7

    Ron68
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    From: Mukilteo, Washington
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    Re: Help: Adding Relays to Headlights

    Might want to check here. This was put together by James W - a long time FYIFORD poster. Complete with pictures.
    http://midnightdsigns.com/james/headlights.htm

    68 coupe - 351W, 4R70W, 9" 3.25 -- 65 convertible - 289 4v, C4, 8" 3.00
     

    12/05/2022 4:17 PM  #8

    BobE
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    Re: Help: Adding Relays to Headlights

    “Here's the diagram I found showing how to wire relays for the stock wiring diagram:
    https://ibb.co/gVgF5Ps”
     
    The above is the wiring I used for my headlight relays.  Suggest using a self-resetting circuit breaker (20amp) instead of a fuse.  I mounted my relays where the voltage regulator had been.  I did not use weather proof connectors on the relays, but that is a good idea.

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    12/05/2022 5:58 PM  #9

    6sally6
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    From: Surfside Beach,SC
    Registered: 4/02/2013
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    Re: Help: Adding Relays to Headlights

    Bullet Bob wrote:

    Red wire to the battery (starter solenoid) THROUGH A 20 AMP FUSE!

    BB1
     

    Why run a 20 AMP fuse when using relays?!
    Ain't that like a belt & suspenders?!
    Maybe you can hep me see-the-light! (pun intended)
    6sally6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

    12/05/2022 8:50 PM  #10

    Bullet Bob
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    Re: Help: Adding Relays to Headlights

    Relay is just a switch, Sal.  Same logic as running a fuse in the hot leg to the radio, or any other device.  The fuse protects all of the circuit beyond it.  That's why it's best to have the fuses as close to the source (bat-tree) as possible. 

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    12/06/2022 9:37 AM  #11

    BobE
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    Re: Help: Adding Relays to Headlights

    Bullet Bob wrote:

    Relay is just a switch, Sal.  Same logic as running a fuse in the hot leg to the radio, or any other device.  The fuse protects all of the circuit beyond it.  That's why it's best to have the fuses as close to the source (bat-tree) as possible. 

    Sal - in addition to BB's response, the headlight switch now will power only the relay coils, reducing the current draw significantly on the 50+ year-old headlight switch. The 20 amp wire will power the headlights. 
     

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    12/06/2022 1:15 PM  #12

    wsinsle
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    Re: Help: Adding Relays to Headlights

    Red wire is 30
    Black wire is 85
    White wire is 86
    Blue wire is 87

    Is that what you are asking?

    Last edited by wsinsle (12/06/2022 1:16 PM)

    If this forum can't fix it, it isn't broke.
     

    12/07/2022 9:06 AM  #13

    TremendousWand
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    Re: Help: Adding Relays to Headlights

    wsinsle wrote:

    Red wire is 30
    Black wire is 85
    White wire is 86
    Blue wire is 87

    Is that what you are asking?

    I found the information finally.  I'm getting it wired up.  thanks

       •Thread Starter
     

     

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