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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

blinking idiot light

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Old Nov 22, 2015 | 05:52 PM
  #1  
bert cook's Avatar
bert cook
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blinking idiot light

i have an 81 f100 with idiot lights.and just noticed that the little battery pic was blinking at me.but when i turn on any thing electrical it stops blinking and goes dark like it should.
 
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Old Nov 23, 2015 | 11:07 AM
  #2  
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Check battery with the truck running. This will tell you what the alternator is putting out. 14 or higher is good.
 
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Old Nov 23, 2015 | 06:48 PM
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Exciter current to the alternator passes through the idiot light when the key is first turned to run.
When the engine is started and the alternator is turning out power, voltage should be equal on both sides of the filament and the light goes out.
If it takes a load to cause the alternator to start charging I would suspect the regulator first.
 
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Old Nov 23, 2015 | 11:05 PM
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i hope its not the reg it dont have 4days on it
 
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Old Nov 24, 2015 | 06:55 AM
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Did you replace the regulator *because* the light was flickering?

Is the alternator original to the truck?
 
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Old Nov 24, 2015 | 12:46 PM
  #6  
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Originally Posted by bert cook
i hope its not the reg it dont have 4days on it
What brand regulator did you put in?

I ask because when I replaced the alternator and voltage regulator on my 1980, I had some weird behavior with my idiot light as well...and it didn't go away until I replaced the NAPA Echlin regulator with a proper Motorcraft one.
 
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Old Feb 13, 2026 | 05:21 PM
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Just found this post, did you get the issue figured out? My truck has a "SEARS" volt. reg.
I wonder how long ago they quit making them.
 
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