Flickering Lights
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Freshman User
Joined: Feb 2013
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Flickering Lights
Hello- truck is a 77 F250 4x4, this is well worn truck and the P.O. didn't know much about anything. Over the last couple days all of the lights controlled by the headlight switch have began to flicker. I replaced the headlight switch today but the lights are still doing it, just not as bad. If I turn on the lights I can hear what sounds like a relay or circuit breaker firing near the headlight switch. Not sure where to go from here.
Any ideas?
Thanks
Lute
Any ideas?
Thanks
Lute
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The clicking you hear is the circuit breaker inside the headlight switch interrupting; this is happening because you have a short in the wiring downstream of the switch. Check the wiring out to the headlights as well as running lights on all four corners for pinched or frayed insulation. There was likely nothing wrong with your old headlight switch.
Junior User
Joined: Aug 2010
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I have this same issue now. I was towing a 20 ft enclosed trailer across country and one night it didn't flicker at all. Next night it did, but also flickered the trailer lights too. How warm do the headlight switches get? I took off my dash cover to put some grease on the headlight switch contacts and just left the cover off. Touched the switch while driving and it was piping hot.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I have this same issue now. I was towing a 20 ft enclosed trailer across country and one night it didn't flicker at all. Next night it did, but also flickered the trailer lights too. How warm do the headlight switches get? I took off my dash cover to put some grease on the headlight switch contacts and just left the cover off. Touched the switch while driving and it was piping hot.
Fleet Mechanic
Joined: Jan 2012
Posts: 1,668
Likes: 13
From: Saskatchewan
The clicking you hear is the circuit breaker inside the headlight switch interrupting; this is happening because you have a short in the wiring downstream of the switch. Check the wiring out to the headlights as well as running lights on all four corners for pinched or frayed insulation. There was likely nothing wrong with your old headlight switch.
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Freshman User
Joined: Feb 2013
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Thanks FMC400, I will check it out now.
Dig'umz- all lights controlled by the headlight switch turn on and off together.
lute
Dig'umz- all lights controlled by the headlight switch turn on and off together.
lute
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Freshman User
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Excellent advice FMC400, after checking each bulb and bulb group I was able to determine it was a wire controlling the rear lights (badly spliced many times with a trailer brake setup and extra lights). The factory hot running to the back had been cut under the cab and was grounding against the body/frame. It was running power backwards from the lights and grounding the circuit. Insulated the wire with a crimp wire nut and the issue was resolved.
Next project- turn signals...
Next project- turn signals...
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Posting Guru
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A wire nut or a butt connector? Either way, you may end up with trouble there again.The best way to fix the wire would be to solder it and then cover it with shrink tubing. A crimp on connector will work, but it will end up corroding and giving trouble. If you stay with that, I'd coat it with dielectric grease and cover it with shrink tubing. That will help keep moisture out.
Good luck, and welcome to FTE.
Good luck, and welcome to FTE.
Junior User
Joined: Aug 2010
Posts: 90
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fmc 400,
i did read your post and i'm going to trace wires. i didn't explain myself well. There is no way to hear any clicking from the circut breaker because of engine and trans noise.
I hooked up my trailer the night before i left to calibrate the trailer brakes, thats when i had seen the flickering for the first time. The next two nights of driving there was no flickering. Then the last night of driving it was flickering bad. I was at a rest stop at 9pm at night, 100's of miles from home. Thats why i greased the contacts in the headlight switch hoping that would do it.
i did read your post and i'm going to trace wires. i didn't explain myself well. There is no way to hear any clicking from the circut breaker because of engine and trans noise.
I hooked up my trailer the night before i left to calibrate the trailer brakes, thats when i had seen the flickering for the first time. The next two nights of driving there was no flickering. Then the last night of driving it was flickering bad. I was at a rest stop at 9pm at night, 100's of miles from home. Thats why i greased the contacts in the headlight switch hoping that would do it.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
fmc 400,
i did read your post and i'm going to trace wires. i didn't explain myself well. There is no way to hear any clicking from the circut breaker because of engine and trans noise.
I hooked up my trailer the night before i left to calibrate the trailer brakes, thats when i had seen the flickering for the first time. The next two nights of driving there was no flickering. Then the last night of driving it was flickering bad. I was at a rest stop at 9pm at night, 100's of miles from home. Thats why i greased the contacts in the headlight switch hoping that would do it.
i did read your post and i'm going to trace wires. i didn't explain myself well. There is no way to hear any clicking from the circut breaker because of engine and trans noise.
I hooked up my trailer the night before i left to calibrate the trailer brakes, thats when i had seen the flickering for the first time. The next two nights of driving there was no flickering. Then the last night of driving it was flickering bad. I was at a rest stop at 9pm at night, 100's of miles from home. Thats why i greased the contacts in the headlight switch hoping that would do it.
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