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Hello everyone, I have a 98 F-150 4.6, today when I was driving my ABS light came on. Then I noticed my battery guage was down at the bottom, around 8v. Then I put on my blinker and all of the guages went to the bottom. I stopped at the nearest parts store to check the battery and the voltage was low. Put in new battery and off I went, all guages and everything was fine. Well, I started thinking about it and thought was it the battery or alternator. I went and checked the voltage at the battery with the engine iff and got around 12.5v, with the engine running at idle not quite 13v. With a working alternator I should have 14.5v correct. poss. bad alternator?
You can tell if the alternator is working by running the truck at idle and turning the lights and blower motor on. The gauge will dip but should recover and compensate for the load. If it can't hold it and goes below 12 then I would check it.