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Driver's headlight on/off by itself?

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Before I go nuts, and pull that grill for a fifth time...


It's not a bulb, only affects the one side (driver's).  Have tested the bulbs, replaced the bulb, twice.


Obviously not a fuse...checked them anyway...


The relay only powers both headlights, so if one works the relay is good.


It will turn itself off and back on while sitting there, just like someone turns a switch on/off.  I have worked the harness to see if there is a wire broken...made no change.


Is there a known cause for this?  My next step is a Dealer...I've exhausted my abilities.

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  • 3 weeks later...

Is there a computer control that can control the headlights independently, or is it simply the headlight switch, through the relay, and then out through individual fuses to each headlamp?


I still have that one floating on/off, for no reason.

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Try checking the quality of the power and ground going to the light. How is the high beam on the drivers light? Does that have a problem lighting itself?


I doubt your female ends on the connector going into the bulb are spread apart to make it a loose connection that is dropping your light out but double check that.


Did you change the bulb with HID or LED's? I upgraded my 2014 to HID projectors and found when it gets colder than 30 outside, it will fail to fire the light on the drivers side when my voltage was above 14.4v. It turned out my ballast was faulty and I swapped it and it has been perfect since. Try seeing if the issue is any better when you have the lights on with the truck off.


The headlights will be getting a pulse width modulated signal on the normal mode when daytime running lights are on and it will give a full battery voltage at night or when you turn the knob manually.


Something to try would be to take the light and swap it between sides, plug your passenger side light assembly on the drivers and see if the issue is still present on the drivers side. If it is then my next guess is a wiring problem or a problem with your body control module since that is what gives the PWM signal to the lights for your DRL.


Try double checking your wiring under the dash for the body control module and make sure it isn't burned or loose. I don't know if it has an independent wire for drivers and passenger. If it does have independent wire, you can wire an external relay and hook it to the passenger side and it should stop your problem since the trigger is coming from the passenger side for the drivers light at that time.

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  • 1 month later...


Ok, I now buy that battery comment.


It dawned on me yesterday that the computer in these trucks can control each headlamp individually although they are tied to a common relay.  Found this out, or more accurately remembered it, doing the TPMS relearn. 


In the linked thread, I did in fact lose one of the two batteries shortly after this headlight issue.  Since I have replaced the batteries, I have not had a single instance of the headlight dropping out. 


So in conclusion, the truck was likely telling me that I had a failing battery.



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  • 1 month later...

Update, still chasing it...


I did add a relay triggered off the passenger's low beam, which required a diode to prevent it creating a loop (pass headlight turns the relay on, the relay backfeeds the driver's circuit, the relay won't shut off). 


So after I figured that all out, I thought I had solved the issue. 




I have now determined the issue is the passenger's low beam ground...the relay puts reliable power to that headlight, it still dropped out.  So I added a ground tonight and pulled the relay as a test for a few days.


Anyone tell me where the ground is for the headlights?  I pulled, sanded, and put anti-corossion paste on all of them I could find when the truck had nearly zero miles.  The truck is oil undercoated so no rust issues.  Either I missed it, or I have a wire or connection pulled apart somewhere. 


Oh, and it is intermittent, so when you pull it apart to start testing, it works and you can't trace it out.

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  • 3 weeks later...

Although there was no indication the harness is bad, the deal finally failed completely.


The way it is wired, there is only one way it couldn't have power and that is if the short harness at the headlight was bad. 


So $50 later, a new harness solved the issues.  Hopefully this helps someone down the road.

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