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On my drive home from work yesterday I noticed my battery light on & the voltage gage pegged high. Came to a stop light, voltage returned to normal, light went out. At first acceleration, light on & high voltage. I turned on everything I could (headlights, AC, etc) & this held voltage normal until I got to the Sears garage who tested the battery. Battery good & something is overcharging....probably alternator but he couldnt test it. I made it home & decided to remove the alternator & take it in for a bench test. Tested good at both Autozone & Pep Boys. Got home, cleaned & tightened all connections & problem did not reappear until this afternoon. Same thing.
I've never seen a high voltage fault before. I'm also confused with the intermintent times it happens. Only when I get RPM's near 2000 & there is no load elsewhere. This is a stock XL with no electrical options.
Any and all advice is appreciated.
if it helps:
2003 Ford F-150 XL
4.2 6-cyl, manual transmission 48000 miles
I don't know how much they are, but you may want to try an alternator anyway. If we assume all the connections are good, and I think you have an internally regulated alternator, it may be a heat related fault that will not show up after it cools off and you take it to the store.
Just to be sure, have someone watch the guage while you go out and wiggle the wiring and the connections(don't get caught in the belt!) to see if you can make it fail.
Mine did this and I went bonkers trying to figure it out. Everything I found was problems with undercharging. Any how, try running a seperate ground from alt. to frame or metal body part, takes maybe 10 minutes tops and worth a try. It fixed my problem.
[I probably wouldn't have listened to this suggestion cause I know it is supposed to get it's ground by being bolted up, but I was at my wits end... It's worth a shot]
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