Alternator going bad again?
Postmaster
Joined: Aug 2003
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From: St. Peter
I say its fine. My 85 F150 does it,and our 94 ranger did it.
The ignition system, headlights, tail lights, cd player, interior lights, blower motors, ecm, etc are things that will draw a little bit of power. It is expected for your lights to dim.
how many watts are your headlights? 60? 60 watts/12 volts = 5 amps per headlight. so thats 10 amps, plus all of your exterior lights, plus your blower motor, and everything else, you are probably drawing alot of current.
The ignition system, headlights, tail lights, cd player, interior lights, blower motors, ecm, etc are things that will draw a little bit of power. It is expected for your lights to dim.
how many watts are your headlights? 60? 60 watts/12 volts = 5 amps per headlight. so thats 10 amps, plus all of your exterior lights, plus your blower motor, and everything else, you are probably drawing alot of current.
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Senior User
Joined: Jun 2007
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From: Darby, PA
Originally Posted by MisterCMK
To the OP - That sounds about right. I think your truck has a 95 amp alternator. If you have any extra things, such as an electric fan conversion, additional lights, etc then you will not have enough juice at idle. At cruise the alternator is outputting enough to satisfy the demand.
Fleet Owner
Joined: Mar 2003
Posts: 24,724
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From: Blue Hill Township
My Explorer does the same thing. Its nothing to worry about. She really gets dim when it is night time, I have the lights on (i have a visor so there are more lights), electric fan turns on, power inverter is on and the defrost is running. 
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Senior User
Joined: Jun 2007
Posts: 101
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From: Darby, PA
Another update.
Got another alternator( no cost as I have lifetime warr) and all is good. I got 14.7 volts at battery with car at idle at about 1200 rpms (Not fully warmed up). 14.6 volts in drive with RPMs at approx 1000 and with all lights and fans on volts were 14.4. Volt gage doesn't move from dead center! All is good for now!
Got another alternator( no cost as I have lifetime warr) and all is good. I got 14.7 volts at battery with car at idle at about 1200 rpms (Not fully warmed up). 14.6 volts in drive with RPMs at approx 1000 and with all lights and fans on volts were 14.4. Volt gage doesn't move from dead center! All is good for now!
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Joined: Jan 2004
Posts: 13,851
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From: SW Va
OK, good feedback & to hear you finally got this one solved. Thanks for closing the thread out.
Sounds like that last alternator had problems, as it should have been able to handle the lights load at idle, anyway it's history, as it should be!!!! lol
Sounds like that last alternator had problems, as it should have been able to handle the lights load at idle, anyway it's history, as it should be!!!! lol
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phoneman91
1987 - 1996 F150 & Larger F-Series Trucks
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May 6, 2010 04:22 PM
