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Interior and exterior lights keep flashing

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Old 06-18-2018, 11:46 PM
dentside22
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Interior and exterior lights keep flashing

Hey so if anyone could help I would really appreciate it. So I have a 1977 f250 and my interior lights including gauges and cluster gauges keep flashing on and off and my exterior lights keep flashing too . It happens after a couple minutes of driving and it keeps flashing on and off
anyone know what the cause is , itís really annoying. Thanks
 
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Old 06-19-2018, 04:47 AM
Shawner1974
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Sounds like an issue I had with grounds. My lights would flicker and the blower motor would draw down when I would leave for work, or I hit large bumps. I installed a voltmeter and could see that the voltage was dipping to 11 volts, with 13 volts at idle. I ended up running a ground cable from negative terminal on battery to a bolt on inner fender well, and another from engine block to the frame. Also checked to make sure my ground straps to my hood and firewall were ok, as well as ground from negative battery terminal to engine block. Fired it up and had 14.5 volts and no more flickering.
 
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Old 06-19-2018, 08:24 AM
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It would have to be all the grounds at once to cause that and I don't see that happening.
But do check & clean them all.

I say head light switch as that is the only thing I can see common to it all.
Dave - - - -
 
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Old 06-19-2018, 09:32 AM
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Originally I too thought it was headlight switch. After replacing that, the dimmer switch, and installing the headlight relay, I still had flickering lights. Check grounds first before throwing money at it like I did. Just because you have a good ground to the engine block from the battery doesn't necessarily mean you have a good ground to the body, and all those lights ground to somewhere. One ground can cause these symptoms, especially if all the lights ground to body and you have no body ground. One $5 battery cable from negative post to the body cured all my ills. Even my gauged work more consistently now. Good luck!
 

Last edited by Shawner1974; 06-19-2018 at 10:51 AM. Reason: Add info
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Old 06-19-2018, 11:46 AM
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Flashing fully off then back on is usually caused by the self resetting circuit breaker in the lighting circuit. It's normally on the headlight switch itself but I'm not sure if it even exists on these trucks. I don't see one on the pics that come up when I search for 1977 F250 headlight switch. And I don't see one on the wiring diagram either.

Flicker can be anything from an open diode in the alternator to Shawner1974's $5 battery cable to a poor ground connection.

Michael
 
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Old 06-19-2018, 04:28 PM
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I had this problem with my 79 years ago. Turned out there was a trailer wire harness tucked up in the frame, & the insulation on one of the wires rubbed thru & was grounding out to the frame. This would trip the circuit breaker in the headlight switch, & the lights would go out. After a short time the breaker would reset & the lights would come back on.

Start at one end of your truck, carefully inspecting each & every wire in the light harnesses. Eventually you'll find a bad spot, usually in the last 12" of wire you look at. There is a plug in the rear harness for the tail lights. You can unplug this harness & see if the problem goes away. If it does, you know the fault to ground is in that harness. If it doesn't go away, you know that harness is good & you won't have to inspect it too closely.
 
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