alt light comes on
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New User
Joined: Sep 2004
Posts: 5
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alt light comes on
The dash alt light turns on and off after the engine starts and after the glow plug time out period. The voltmeter always reads about 14 or so volts when this happens. After the engine is warm, the frequency on & off is less, like on for 10 seconds and off for a couple minutes. I had this problem for a week or so and now its gone the past two days. What's happening and what do I need to fix or replace?
Logistics Pro
Joined: Jul 2001
Posts: 4,137
Likes: 41
From: Marble Falls, Texas
Pull the three wire plug on the alt. Pull the plastic lock that keeps the pins in the connectors. Clean and slightly crimp the pins, re-install pins in the connector. Put lock back in and re-install plug. Say goodbye to the problem. These connectors are prone to this "flashing" battery light because everyone leans on them while working on the truck or just corrosion. Before you do all this, you can test my theory by turning on your parking lights with the truck running and go wiggle the wires in the connector. I bet you will see the lights get bright and dim. Try that out and if it doesn't cure it, I'll go deeper for you. i.e. the regulator can be replaced for alot cheaper than the alt. But when you pull the regulator, look at the shaft inside the alt where the bushing for the regulator run. If they are worn down, it's alt time. If not, a regulator will cure your problem most of the time. Hope that helps.
Elder User
Joined: Nov 2005
Posts: 555
Likes: 0
From: Cincinnati OH
about two months after buying my truck and not knowing yet all of the common failures i had this problem. i went to my local pepboys in PA at the time and pulled the alternator right there in their parking lot and took it in and had them bench test it. it came up good. guy at store explained the usual problem to me. i went back out and reinstalled the alternator, never a problem since. i guess for me all it took was unplugging and plugging the connector back in.
New User
Joined: Nov 2007
Posts: 14
Likes: 0
From: Minneapolis
This sounds similar to my problem. The voltmeter bounces back and forth from about 11 to 14 during my enitre drive, long after truck is warmed up. I'm going to try that solution of cleaning the connector. Thanks for the tip.
New User
Joined: Feb 2008
Posts: 8
Likes: 0
I had the same problem with my truck not long ago. I tried unplugging the connector to my altenator but that didn't work for me. I found that there is a relay that is in the charging circuit that activates the light. I replaced the relay for $5 and the problem was gone. So check the altenator first, if it isn't that the you can find the relay on the passanger side fender.
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