Cannot believe these instruments
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Junior Member
Joined: Mar 2018
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Cannot believe these instruments (ammeter, charging light)
2004 XLT 5.4: Went through some electrical problems recently, and want to pass along a relevant observation.
Of course, I have to deal with the excessive phantom drain, which I gather is normal for these things. I see 1.5 Amps (18 Watts) being sucked out of my battery when everything is "off."
But along with that, the charging system was not doing its job. It wasn't charging at all. So that suggests a bad alternator, which is exactly what the problem was. I bought a new Remy 110 Amp alternator from Rock Auto (for about half the price of remanufactured factory units), and that solved that problem. I did an autopsy on the failed unit and found the inboard slip ring was destroyed, and actually in pieces.
But the reason I'm writing this is to point out a disturbing phenomenon. All the time I was driving around with a totally useless alternator, the charging idiot light would extinguish, like it's supposed to, and the ammeter indicated that positive charging was going on. Right up to the point where the truck just stopped dead because there were no more electrons available. I don't know where this ammeter gets its information, but it is clear to me that I can never trust what it says.
Of course, I have to deal with the excessive phantom drain, which I gather is normal for these things. I see 1.5 Amps (18 Watts) being sucked out of my battery when everything is "off."
But along with that, the charging system was not doing its job. It wasn't charging at all. So that suggests a bad alternator, which is exactly what the problem was. I bought a new Remy 110 Amp alternator from Rock Auto (for about half the price of remanufactured factory units), and that solved that problem. I did an autopsy on the failed unit and found the inboard slip ring was destroyed, and actually in pieces.
But the reason I'm writing this is to point out a disturbing phenomenon. All the time I was driving around with a totally useless alternator, the charging idiot light would extinguish, like it's supposed to, and the ammeter indicated that positive charging was going on. Right up to the point where the truck just stopped dead because there were no more electrons available. I don't know where this ammeter gets its information, but it is clear to me that I can never trust what it says.
Last edited by gjgerhard; Aug 7, 2019 at 07:58 PM. Reason: Make title more specific
5 Year Member
Joined: Apr 2019
Posts: 1,789
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From: Wichita Falls, TX
Its a volt meter, and not an ammeter. It measures voltage from the alternator, but when the truck is off, it shows battery voltage (I know because I checked this out on a near dead battery and watched the meter slowly move to the left when I had the AC fan running, by then I couldn't start the truck. Oops. (this was in 2011, if I remember correctly)
