voltmeter jumping

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Nov 29, 2012 | 06:52 PM

91f150302

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Joined: Oct 2012

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voltmeter jumping

I have a 1991 f150 with a 5.0 and 5 speed. this problem just started today and has never done this before. i was driving around today and the voltmeter spiked past the 18 volt mark for a second and the battery light came on. the needle went back to normal and battery light came off. it has never done this before and did it probably 10 times in about 30 minutes. i did notice after it started doing this that the voltmeter was reading higher then it normally does. it was staying on the L in normal after the problem first occured where as my needle typically stays around the M.

My first thought is that the alternator is going bad. i also know that the guage clusters in these trucks are known for false readings and about a month ago my fuel guage started acting up and not reading correct and it would jump or stay in one spot and never move. this is also making me think that some of the guages are bad and the alternator could be fine.

I would just like to know if I am on the right track or if there is something else it could be. Thanks.

Nov 29, 2012 | 07:05 PM

Evan_P

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Joined: Mar 2012

Posts: 3,507

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From: Oregon

Well there may be an issue with the gauge, but I wouldn't count on that. To me it sounds more like a bad voltage regulator.I would hook a volt meter up to the trucks battery and fire the truck up. Monitor the reading for a little but and see it it spikes as well. This is basically to rule out the gauge being bad. If it spikes as well then its not the gauge, and more likely the voltage regulator.