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Freak of Nature
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Discussion Starter #1
Here's the issue with my 1996 F250 7.3. Truck has a brand new alternator from what I can tell the alternator is working fine. 14V off the main wire, then I have 14V at the plug except the middle wire which is 7V. The problem is the gauge in the dash is reading low and dims when the headlights are turned on. I have the ford hi idle box which tells me the voltage and it will jump back and forth from 11V to 13.8V. it used to always read a steady 14.2V.
 

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It could be a defective voltage regulator in the 'new' alternator. Had it happen to me once. Are your batteries in good shape? A weak cell can cause these same issues. Check each cell with a hygrometer.
 

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14V off the main wire...the gauge in the dash is reading low and dims when the headlights are turned on.
So, what is the voltage in the dash? Measure at the cigar socket, and the aux. socket. Also measure across the battery posts.
 

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Freak of Nature
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51 Posts
Discussion Starter #4
brand new batteries with alternator change. And like I said it seems to be sending correct voltage from the alternator, just the gauge seems to be hinky. I have checked and the batteries are staying charged. I have also cleaned the connection on the cluster as well.
 

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Freak of Nature
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51 Posts
Discussion Starter #5
So, what is the voltage in the dash? Measure at the cigar socket, and the aux. socket. Also measure across the battery posts.
That I have not checked. I'll do that in the morning. I should have 12V at the cigar socket and the aux, correct?
 

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Freak of Nature
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51 Posts
Discussion Starter #6
Todays update. Went over all the grounds I could find made sure they were all clean and tight. checked voltage at aux socket and cigar light 11.6V not running. 13V running. any ideas would be helpful at this point I'm starting to think it might just be the gauge that's screwed
 

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If you're getting 14V at the alternator output, but only 13V in the dash, there's high resistance between them. Sounds like the gauge is working perfectly, and indicating a real problem. I'd start by removing all the terminals from the battery side of the starter relay, polishing them, and applying a THIN layer of MotorCraft Electrical Grease Amazon.com: Genuine Ford Fluid XG-12 Electrical Grease - 3 oz.: Automotive to each one and the relay terminal, before stacking them back on.
 
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