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Old 08-18-2021, 05:31 PM   #1
pbr
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Join Date: Oct 2011
Location: new york
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tail lights stop working after starting up the truck

My brake lights and tail lights stop working shortly after I start the truck. I seams like the voltage goes up due to the alternator charging and the brake lights lite the parking lights and the parking lights stop working. Shortly after shutting the truck off the lights return to proper working order. I had LEDs and have removed them and went back to regular bulbs I had the same problem.

I haven't had a chance to test the entire system yet and was hoping some one here might have had this problem before. I will go through the system starting with the grounds. I don't know if the increase in voltage is causing the ground to be insufficient.

Thanks
Patrick
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Old 08-25-2021, 02:15 PM   #2
RustyPile
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Re: tail lights stop working after starting up the truck

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Originally Posted by pbr View Post
My brake lights and tail lights stop working shortly after I start the truck. I seams like the voltage goes up due to the alternator charging and the brake lights lite the parking lights and the parking lights stop working. Shortly after shutting the truck off the lights return to proper working order. I had LEDs and have removed them and went back to regular bulbs I had the same problem.

I haven't had a chance to test the entire system yet and was hoping some one here might have had this problem before. I will go through the system starting with the grounds. I don't know if the increase in voltage is causing the ground to be insufficient.

Thanks
Patrick
Classic symptoms of a loose connection somewhere.. Engine running and truck moving "rattles" the bad connection and lights quit working.. Turn off the engine, vibration stops, the bad connection stabilizes, and the lights work again.. Brake lights and park lights are 2 separate circuits so if you're loosing power to these lights, more than likely you have 2 separate problems.. If the problem is only with the lights at the rear, I'd suspect a bad bed-to-frame ground connection.. Same goes for the front lights, look for a bad ground. It's almost impossible to say just where the problem lies, it could be almost anywhere.. Good electrical troubleshooting skills go a long way..
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Old 08-25-2021, 03:44 PM   #3
pbr
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Re: tail lights stop working after starting up the truck

I suspect itís a ground because Iím getting 14v with the truck running at the bulb. It seams to take a bit and it seams to be when the alternator is marking voltage so that also makes me wonder if the ground canít handle the higher voltage but when itís 11.5 to 12.5 volts the ground is handling it. I just need some time to go though all the grounds and wiring.
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