Battery dash light
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
If the light is on, a lot of times it is caused by a loose connection on the single wire that plugs into the top of the alternator. That is the "charge" signal wire from the PCM and if it is loose the alt won't charge. Have someone wiggle that wire while you watch the gauge / light and see if they fluctuate.
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
Unless that is the wire that just signals to the battery light. Seems odd that there would be a separate wire to the Alt just to turn on the battery light wouldn't it? I guess I don't know for sure, but that is definitely the wire that the light signals off of. I assumed it went to the PCM but I guess I don't know for sure.
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
So it does go directly from there to the dash! Lol. I stand corrected! Leave it to those electrical engineers at Ford....
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Elder User
Joined: Aug 2009
Posts: 869
Likes: 1
From: Michigan
If the light is on, a lot of times it is caused by a loose connection on the single wire that plugs into the top of the alternator. That is the "charge" signal wire from the PCM and if it is loose the alt won't charge. Have someone wiggle that wire while you watch the gauge / light and see if they fluctuate.
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Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
Alternators need an initial field current to get started. The field current is supplied through that light shown in the diagram above. Note that when you first turn the key ON the light is on. That is because the top connection of the light is at battery voltage and the bottom connection of the light is effectively at ground, through the field coil in the alternator. The purpose the the resistor across the light is to supply enough field current to start the alternator in case the lamp burns out. If the alternator is not putting out enough voltage, once started, then the bottom connection of the light is at less voltage than the top so the lamp may come on but at different intensities depending on the voltage differences across the bulb. Also the alternator is always charging, it just doesn't seem so when the glow plugs are on because they draw an enormous amount of current.
Elder User
Joined: Aug 2009
Posts: 869
Likes: 1
From: Michigan
this happened to my nephews beat up f150 but his wasnt charging at all. it turned out to be the cluster. we werent getting the signal to turn on the regulator at all. I ended up just putting a jumper wire across the plug that went into the cluster. its charging just doesnt have a charge indicator anymore. but it a rusty old daily beater so he didnt care.
Elder User
Joined: Aug 2009
Posts: 869
Likes: 1
From: Michigan
https://www.ford-trucks.com/forums/1030328-tech-mod-info-links-4.html#post11383134
Other wiring diagrams for our trucks. a lot of electrical problems can be figured out by having a roadmap of how its supposed to be. these diagrams show fuses and their sizes and position in the fusebox. these diagrams also show grounds and where they are connected to the chassis. so if youre having a problem with a specific circuit you can find out where the ground is supposed to be located and you can check its integrity. all you need is a volt meter.
Other wiring diagrams for our trucks. a lot of electrical problems can be figured out by having a roadmap of how its supposed to be. these diagrams show fuses and their sizes and position in the fusebox. these diagrams also show grounds and where they are connected to the chassis. so if youre having a problem with a specific circuit you can find out where the ground is supposed to be located and you can check its integrity. all you need is a volt meter.
Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
this happened to my nephews beat up f150 but his wasnt charging at all. it turned out to be the cluster. we werent getting the signal to turn on the regulator at all. I ended up just putting a jumper wire across the plug that went into the cluster. its charging just doesnt have a charge indicator anymore. but it a rusty old daily beater so he didnt care.
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Posting Guru
Joined: Aug 2002
Posts: 1,729
Likes: 2
Thanks for all the replies!! I haven't had a chance to check the connector yet but I'm sure thats where the problem lies as it acts up everytime I crawl up on the engine to work. Atleast now if it's in the plug I know how to bypass!
Lead Driver
Joined: Oct 2003
Posts: 8,476
Likes: 37
From: Madison, WI
The other takeaway from Ken's diagram is that there is NO connection between the PCM and the alternator; I often see threads of guys chasing their tails thinking that the PCM hasn't "turned on" the alternator, when there's no such bird.
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