Truck not charging issue, battery light on (97 4.6L)
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Junior Member
Joined: Jan 2010
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Truck not charging issue, battery light on (97 4.6L)
It all started...
...when I got onto the highway and glanced down at the gauge cluster and noticed my battery light was on and kind of flashy (clipping, so to speak)...and that I was in 2nd gear...whoops. (My tach's busted, else I probably would have noticed that sooner.)
Quick correction and things are right as rain. The next day I go out and make 3-4 stops with less than 10 minutes of drive time between each. I'm almost home (battery light's been on intermittently since last night) and the idle slows slightly and the windows no longer work. I make it home and the gauge cluster is dead by now, but leave the truck running, grab a socket wrench and pry off the positive battery lead. Truck dies.
I'm thinking alternator, so I pull the battery and charge it inside, then pull the alternator the next day and have it tested. Tests fine (putting out 1430 (is that mA?) per O'Reilley's). Crap; so much for that idea. Cleaned all connections (including taking off the negative terminal grounded to the starter and shining it up a little, then pulling the connections off the firewall and sanding them lightly), checked 20A inline blade fuse, both 175A fusible links, but it's still not charging. If I want to go anywhere, I have to pull the battery and charge it inside.
I was thinking it might be the voltage regulator, but I just called O'Reilley's and they told me that the test on the alternator included the regulator. I just confirmed that the belt on the pulley is okay.
Please help? What did I most likely fry that caused my battery light to come on?
Thanks in advance.
~Brad
...when I got onto the highway and glanced down at the gauge cluster and noticed my battery light was on and kind of flashy (clipping, so to speak)...and that I was in 2nd gear...whoops. (My tach's busted, else I probably would have noticed that sooner.)
Quick correction and things are right as rain. The next day I go out and make 3-4 stops with less than 10 minutes of drive time between each. I'm almost home (battery light's been on intermittently since last night) and the idle slows slightly and the windows no longer work. I make it home and the gauge cluster is dead by now, but leave the truck running, grab a socket wrench and pry off the positive battery lead. Truck dies.
I'm thinking alternator, so I pull the battery and charge it inside, then pull the alternator the next day and have it tested. Tests fine (putting out 1430 (is that mA?) per O'Reilley's). Crap; so much for that idea. Cleaned all connections (including taking off the negative terminal grounded to the starter and shining it up a little, then pulling the connections off the firewall and sanding them lightly), checked 20A inline blade fuse, both 175A fusible links, but it's still not charging. If I want to go anywhere, I have to pull the battery and charge it inside.
I was thinking it might be the voltage regulator, but I just called O'Reilley's and they told me that the test on the alternator included the regulator. I just confirmed that the belt on the pulley is okay.
Please help? What did I most likely fry that caused my battery light to come on?
Thanks in advance.
~Brad
Technical Article Contributor
Joined: Apr 2009
Posts: 10,697
Likes: 14
From: In the fast lane from LA to Tokyo...
Could be a diode in the altenator....try this>>>click link>>>https://www.f150online.com/forums/4625595-post11.html
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Your missing it.
There are only two parts to the charging system.
The battery and the alternator.
Never try to run the motor on just the alternator. It's a mistake to try that.
.
You need some 101 on the charge system.
Use a voltmeter and check the voltage level at the battery after a startup.
If you do not see at least 15 volts after cranking, the alternator is not outputting.
What puts the dash lamp out is when the alternator is outputting.
The regulator removes the ground from the lamp circuit when output is good.
If you see good charging voltage but the battery goes dead after a short time, a diode in the alternator stack is shorted to ground discharging the battery.
Maybe their test missed it. A condition like this will still charge the battery but drain it when the motor is stopped.
That's all there is to it.
Now take the bull by the horns and shakem up!
Good luck.
There are only two parts to the charging system.
The battery and the alternator.
Never try to run the motor on just the alternator. It's a mistake to try that.
.
You need some 101 on the charge system.
Use a voltmeter and check the voltage level at the battery after a startup.
If you do not see at least 15 volts after cranking, the alternator is not outputting.
What puts the dash lamp out is when the alternator is outputting.
The regulator removes the ground from the lamp circuit when output is good.
If you see good charging voltage but the battery goes dead after a short time, a diode in the alternator stack is shorted to ground discharging the battery.
Maybe their test missed it. A condition like this will still charge the battery but drain it when the motor is stopped.
That's all there is to it.
Now take the bull by the horns and shakem up!
Good luck.