battery light on and alternator is charging

Asked by Oct 31, 2014 at 10:17 PM about the 2005 Ford F-150 XLT SuperCab

Question type: Maintenance & Repair

05 ford f-150 4.6 v8,, after about 5-seconds starting the truck the battery light comes on and remains on during the duration of driving,, I am buying the truck but it already has a brand new alternator installed and a little concerned,, had a mechanic look at it and it is a steady charge of  14v, he then told me that even though it is charging not to rule out it is a faulty alternator,,  ( diodes or going bad ), does that sound about right, can the DIODES GOING BAD cause the battery light to remain on while driving and charging system holding  14v too the battery,,

thanks

3 Answers

106,075

Possibly. Alternator output voltage to high or to low may cause this. But first I would tighten and clean all battery connections. Loose connections can cause this also.

2 out of 2 people think this is helpful.

thanks, forgot to add that while checking for loose connections as you stated while wiggling the wires to the back of alternator not the thicker wire held by a nut but the wire harness that plugs into the alt. fell right out and never was securely plugged in, can that have done something to the alt,, and could the diodes going out in the alt actually cause the battery light to stay illuminated while holding 14v as the mechanic stated or is he on the dealers payroll,,

106,075

Double check that connection. If it's not properly making contact the light will come on.

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