Alternator wiring
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
That capacitor is for Radio interference, and yes if it gets defective it can ground out that wire. Disconnect the capacitor and see what happens, it wont harm anything except radio reception.
I agree with Franklin, make sure the ground to the regulator is good. It grounds through the metal body of the regulator, to the fender.
I agree with Franklin, make sure the ground to the regulator is good. It grounds through the metal body of the regulator, to the fender.
New User
Joined: May 2010
Posts: 11
Likes: 1
Didnt have a lot of time to mess with it today but did remove the regulator and cleaned the screws that hold it on and took some sandpaper to remove some paint. Unpluged the capacitor and still no luck. I just bought this truck and it looks like someone has jacked with the wiring and will have to start tracing things down and look for a short. I will use your diagram to compare to.
New User
Joined: May 2010
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I found that when I unhooked the wire that goes to the volt meter, yellow/black in diagram and yellow/green on my 83, the fluctuating went away. Im assuming my volt meter is bad but getting to it in the dash looks like a pain. Any chance the shunt in your diagram is bad? If so, how do I find it and test it? Not really sure what its function is. Thanks again.
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
unscrew it?
Because your lights dim as the gauge fluctuates, this tells me the gauge is
merely confirming the existence of a problem in the start/charge/run circuitry
that the dimming lights are also telling you about.
You have an ammeter (measures current), not a volt meter (measures voltage).
The shunt basically reduces the amount of current available for the ammeter
signal to help prevent electrical fires in the dash, I really doubt it's your
problem.
But, because your wiring seems to have been jacked with, it's prolly not a bad
idea to check for melted plastic & burnt wiring...
Removing the gauges is fairly straight forward and easy... remove the
headlight & wiper *****, the trim, then the four screws holding the cluster to
the dash. You'll then have to reach behind to disconnect the speedometer cable,
main cluster electrical connector, and the Emissions & 4x4 lights (if installed).
The gauge itself is held in with two nuts that secure it to the white plastic
housing and ensure its connection to the flexible printed circuit. But, I would
think the only thing you'd need to be looking for is melted wiring and/or
plastic so removal isn't necessary.
Nevertheless, if you want to remove it, that's also pretty easy... there are a
bunch of 1/4" screws on the front you'll have to pull the front plastic off, then
unscrew the two rear nuts to pull the gauge out the front.
Others here are better at diagnosing & troubleshooting this stuff than I am so
I'll maybe learn something from those guys, too. Pictures of your under hood
wiring at the alternator & regulator would prolly help.
New User
Joined: May 2010
Posts: 11
Likes: 1
Thanks for the response. Now that you mention it, I do realize its an ammeter. I'll get some pictures up soon. As far as I can tell, the only wiring that isnt factory is the wiring from the alt to the regulator/solonoid/and wiring harness. It is confusing to my small brain and Im not 100% positive that its all correct. Good news is that the truck is working and the alt is charging. Im not above running without a guage as this is only a truck that I plan on keeping local.
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
The shunt is located in the factory wiring between the altenator and the starter solenoid (ie battery). Your ammeter wires are also hooked to each side of this shunt respectfully.
So if this harness is NOT factory original, this is probably where your problems lie. You should find a good factory altenator harness for your truck. This can be very difficult because most are obsolete, and there are numerous different ones in the wrecking yards.
So if this harness is NOT factory original, this is probably where your problems lie. You should find a good factory altenator harness for your truck. This can be very difficult because most are obsolete, and there are numerous different ones in the wrecking yards.
New User
Joined: May 2010
Posts: 11
Likes: 1
I thought I was good after I disconnected the yellow/green wire that seemed to go to the ammeter. I think its the same as the yellow/black in the previous diagram. Come to find out, the fluctuating stopped but so did the alternator charging. It is the factory harness. The only thing that was confusing me was that fusable links had been changed. I do get 12v at the alternator with engine off so I know the links are still good. I am fine without the ammeter but I just want this thing to charge. I then put 12v to the yellow/green wire and then tested voltage at the battery. I found it charging 17v and things started smoking up by the firewall. Not good. That ended my experiment and the good news is I dont think I did much damage as everything still works as before. Is there a way to bypass the ammeter and still make this thing charge? Any suggestions would be greatly appreciated.
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New User
Joined: May 2010
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for what its worth, this guy had the exact same problem.
https://www.ford-trucks.com/forums/4...ectricity.html
https://www.ford-trucks.com/forums/4...ectricity.html
New User
Joined: Jun 2011
Posts: 1
Likes: 0
I was reading this thread. So I thought I would ask. If I posted wrong please forgive me. I am about to say I am done. Have a 1980 F100 with a 302. The charging light on dash is on. So I finally got the bolt broke free and took it to get tested. Test bad got new alt and put it on. Light still on and when I disconnect the pos cable truck stops. Before alt change it would run. On the back is the Batt the Sta and FLA I connected them to what I thought was correct. The orange cap type to FLA the thicker solid to BATT and the black cap 2 lead to STA. Did I mess up? Also changed selenoid. Any help would be appreciated.
Moderator
Joined: Jan 2001
Posts: 56,980
Likes: 2,735
From: Virginia
I was reading this thread. So I thought I would ask. If I posted wrong please forgive me. I am about to say I am done. Have a 1980 F100 with a 302. The charging light on dash is on. So I finally got the bolt broke free and took it to get tested. Test bad got new alt and put it on. Light still on and when I disconnect the pos cable truck stops. Before alt change it would run. On the back is the Batt the Sta and FLA I connected them to what I thought was correct. The orange cap type to FLA the thicker solid to BATT and the black cap 2 lead to STA. Did I mess up? Also changed selenoid. Any help would be appreciated.
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