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Enable/Disable Daytime Running Lights

Thanks to Don Smith for contributing this article. This tech article was originally posted at It is primarily intended for 1990's-2000's Ford trucks but most likely also applies to other Ford models and years.

Why was this article created?
There seems to be a lot of confusion about Daytime Running Lights (DRL)  on the Ford F150 trucks. How to enable them, how to disable them.Can I use the existing wiring harness to do this or do I need the Ford "kit" to do it? Where do I get the parts to enable them? What are the part numbers? The following article was created to help you with enabling or disabling DRL for your truck.

How DRL Works:
1999 and newer:
From the manual: 
The DRL are implemented by using the low beams at a reduced voltage of approximately 80% system voltage. This is accomplished by inserting a DRL resistor in series with the low beam filaments. When the headlamp switch is engaged, the daytime running lamp function is disabled and the low beam filaments receive 100% system voltage.
What it means: The DRL Relay Block enables power to the low beams and the resistor changes the voltage going to the low beams from 12 volts to 10 volts thus making them dimmer. In trucks that do not have DRL a loop-back plug is in place of the Relay Block which provides ground to the Multifunction Switch (Steering Column High/Low/Flash to Pass switch) so the normal low and high beam lights still work.  

1998 and older:  (Sorry people...  very limited information on this one)
From the manual: 
The  DRL system is designed to turn the high beam headlamps on at a reduced output without illuminating the high beam indicator. The system is activated when the ignition switch is in the ON position, the headlamp switch is in the OFF position, and the parking brake is released.
What it means: The DRL "Module" does everything.   It does not use a resistor but instead uses switches to provide lower voltage to the High beams.   Not sure about to much more like wiring, etc. All I know is that it's not compatible with the 1999 and newer layout. I do however have the part number for the module:  F65Z-15A272-AA. It's location is around the same area as the resistor on the 1999 and newer trucks.

Some History of my search...
I have spoken to the service department and parts department at my local Ford Dealership (where I bought the truck) letting them know I wanted to enable DRL on my 1999 Ford F150 truck. I was told that this could be done by purchasing the DRL Kit for about $55.00. I did just that and found that I would have to hack into my wiring harness to get this to work. I checked my shop manual and found the truck is already wired for DRL.I'm making an assumption that this is because Canada requires DRL and Ford does not want to have 2 wiring harnesses for the same truck. So I checked my truck and sure enough, the wiring harnesses are there and all I needed to do is replace the loop-back plug with the DRL Relay Block and install the DRL Resistor into it's location.  
Ford enables DRL on Canada trucks simply by plugging in a DRL Relay Block and plugging in a DRL Resistor.  On American trucks without DRL, the wiring harness is the same but they simply replace the DRL Relay Block with a loop-back plug and put a cap on the wiring harness where the DRL Resistor plugs in. The loop-back plug provides ground to the Multifunction Switch (Steering Column High/Low/Flash to Pass switch) so the lights still work when the DRL Relay Block is not present.  On trucks sold without DRL the DRL Relay block is not present, so the resistor doesn't even need to be plugged in... thus the cap.  So for people wanting to disable DRL on their trucks, all they need to do is remove or unplug the resistor.

I want to Disable DRL on my Truck...
This is actually very easy. You need to find the resistor (See Location is Everything below) and disconnect it.  It's that easy.  And Yes...  your low beam and high beams will still work with the resistor unplugged.  :)

I want to Enable DRL for my Truck...
So you want DRL for your truck but don't want to go out and get the electrical engineering degree needed to install the Ford DRL "Kit"? Well...  you can enable DRL for your truck without hacking into your wiring harness. Use this site to get locations and part numbers for doing this.  There is another good web site out there to help you with this task. See the Other DRL Web Site links below.

Location is Everything!
Finding this stuff seems to be the greatest challenge for everyone. Here is where everything is located on my truck.
DRL Resistor/Cap:
The DRL Resistor (or where it's supposed to be) is located in the front of the truck. Click for Diagrams
DRL Relay Block/DRL Loop-Back Plug:
The DRL Relay Block is located just under the top of the passenger side dash.  Click for Diagrams

Part Numbers:
1999 and newer:
The part numbers depend on the year of truck you have. What I have seen is that Below are the part numbers of the Relay Block and the Resistor:  (The battery and penny give you an idea of size)

Picture of the relay & resistor

Relay Block (Shown Left) - Ford Part Number YL1Z-13B218-AA
Resistor (Shown Right) - Ford Part Number XL3Z-14A601-AA
Cost of the relay block is about $45.00 and the resistor is about $15.00.  So for about $65.00 (including shipping) you can plug in these parts and have DRL on your truck.  :)

1998 and older:

Relay for 1998 & earlier trucks

DRL Module - Ford Part Number F65Z-15A272-AA

Contacting Me!
You can email me at [email protected] if you have questions about this since I've done this on my truck and it works like a champ.

Disclaimer: (Sorry...  I have to get legal for a minute)
What you do to your truck/car is your business not mine.  I am not responsible for damage caused by you or someone else to you or your vehicle by following any or all of these pages. Use at your own risk!  Work on your vehicle at your own risk.  
 All the component location views and wiring diagrams are from the 1999 F-150/250 Shop and Wiring Diagram Manuals distributed by Helm Incorporated.  (I would recommend ANYONE doing work on their vehicle to get the shop manual...  not cheap but they are good!  You can even get them on CD!)

Loop-back plug in detail

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The only numbers I found on the plug were F4SB and 14489-P (Yellow Arrows) though the connector number may be EPC34.  If you can find the plug I'm sure you can make your own loop-back plug.   :)

Loop-back plug close-up

Loop-back plug wires

The red arrows indicate the only 2 metal contacts in the loop-back plug which makes sense since in the DRL wiring diagram you can see that this would provide ground to the Multifunction Switch (Steering Column High/Low/Flash to Pass switch) when the DRL Relay block in not installed.

Loop-back plug wiring colors & location

DRL Resistor Location & Pictures

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This is where the resistor is if DRL is installed.  If not you will just have a cap on the wire harness. The blue arrow points to it's location.

DRL Resistor Location

If you lay on your back with your feet out the front of the truck you can look under the left side and see the wiring harness for the DRL Resistor (This photo is taken from that view). 

The Blue arrow points to the DRL Resistor (Cap shown on mine). The Green arrow shows the wiring harness going to the left headlamp. The Red arrow shows the wiring harness going somewhere else (Never had the time to follow it).  The Yellow arrow shows the Fog Lamp harness

DRL Resistor Picture

DRL Relay Block

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My truck does not have the Relay Block but it has the harness with the loop-back plug. The blue arrow points to it's location. Note: More info on how to access the wiring harness below the diagram

Relay Block Location

You can access the wiring harness from the top of the dash. You will notice an access panel that can easily be removed (Careful not to mess up your dash)

Dash top panel

Dash top panel removal

After removing the access panel, you can see where the DRL Relay block would go: The Red arrow is showing the loop-back plug. The Blue arrow is showing the RPO Relay Block. The Yellow arrow is showing the the harness where the Autolamp module goes (Not even going there!).

DRL Relay Block Photo


DRL Wiring Diagrams

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DRL Wiring Diagram #1

DRL Wiring Diagram #2