# F-550 charging problem.



## STLfirewood (Sep 11, 2009)

My batteries went dead on my truck. I swapped the alt(it tested dead) The new one won't show more then 12.2 on my fluke. It drops a little when you turn the head lights on. Voltage is the same on the back of the alt as it is at the batteries. I took it back to the store and they tested it. Tested good on the bench but bad on the truck. They swapped me another new one and I have the same problem. Where should I look.

Thanks Scott


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## matt9923 (Sep 11, 2009)

STLfirewood said:


> My batteries went dead on my truck. I swapped the alt(it tested dead) The new one won't show more then 12.2 on my fluke. It drops a little when you turn the head lights on. Voltage is the same on the back of the alt as it is at the batteries. I took it back to the store and they tested it. Tested good on the bench but bad on the truck. They swapped me another new one and I have the same problem. Where should I look.
> 
> Thanks Scott



Check for shorted wiers. test form the alt to the batteries and everything in between.


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## STLfirewood (Sep 11, 2009)

Would that change the output at the alt? 

Scott


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## matt9923 (Sep 11, 2009)

STLfirewood said:


> Would that change the output at the alt?
> 
> Scott



Hm a just re-read your post. 

So it bench test's fine and when you bolt it in it tests as bad? Without anythign hooked up? 

I had a truck once with kinda the same problem and the "grounded" frame was getting electricity to it form a short and it was f-in everythign up. 
Im no expert on 550s. So i may just be rambling.


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## gilraine (Sep 11, 2009)

check to make sure you have battery voltage at the small harness on the alternator.. IIRC the field wire is the middle one in the small harness.. sounds like the truck is not exciting the regulator..


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## STLfirewood (Sep 13, 2009)

I checked I have battery voltage at the small wire. I only have a 2 wire plug. I guess I'll take it to the shop. I know it has to be something small.

Thanks for the help Scott


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## thansen (Sep 20, 2009)

I have a 2008 F550 and had charging problems, the warning light kept showing up on my dash and then would go off after driving for awhile. Took it back to the dealer, they did everything, changed the instrument cluster, changed the alternator, 3rd time they found out this truck has two alternators and one of them was just unplugged. I couldn't believe it! I never did pop the hood and look myself because it was under warranty and would just drop it off coming back through town and would tell them to deal with it. But seriously, the mechanics didnt even know and went through all that trouble then waaalaaa pluged in the other alternator and it was fixed!


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## matt9923 (Sep 20, 2009)

thansen said:


> I have a 2008 F550 and had charging problems, the warning light kept showing up on my dash and then would go off after driving for awhile. Took it back to the dealer, they did everything, changed the instrument cluster, changed the alternator, 3rd time they found out this truck has two alternators and one of them was just unplugged. I couldn't believe it! I never did pop the hood and look myself because it was under warranty and would just drop it off coming back through town and would tell them to deal with it. But seriously, the mechanics didnt even know and went through all that trouble then waaalaaa pluged in the other alternator and it was fixed!



sad the dealer didn't know their was 2 alternators?


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## thansen (Sep 20, 2009)

Yea, it was pretty ridiculous. It seems dealers are just parts replacers more then mechanics anymore. They actually tore the dash apart and put in a whole new instrument cluster blaming the idiot light. When I found out about the 2nd alternator and they just had to plug it in, I grabbed the keys and walked out laughing.


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## flashpuppy (Sep 20, 2009)

I have an 01 F550. Nothing but charging problems. The battery light started flickering on the dash. Now it is just always on. There is a green with red tracer wire that I need to trace through the harness. Very common problem as per the TSB.

Seems like these SuperDuty's have quite a few faults in the charging system. I would say to start testing continuity of all the wires. You have to have a short somewhere.

What year F550?


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## kevlar (Sep 21, 2009)

it should charging at 14.5. is the truck a diesel? My bosses truck is and after we replaced the alternator it takes time for it to start charging. also we used a napa alternator but it didn't last,the ford one is the best (I know pricey but it is true!)


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## lt1nut (Sep 21, 2009)

I pm'd a Ford truck tech I know from a different forum, giving him the addy for this thread. I asked if he'd be willing to help you guys since he knows Ford truck stuff very well and doesn't mind helping folks over there even though it's not a Ford or truck forum.

I HOPE he can help y'all....


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## Redneck (Sep 21, 2009)

Haaaaaaaaaaaaaaay the Hillbilly is here.

I'm the tech the above poster is talkin' about.

Is this truck a diesel or a gasser?

There is a 2 minute delay on a diesel truck after startup before it hits the alternator to turn it on, since you don't want to feed the glow plugs 14v, they don't care for that too much.

2 wires on the alternator at the top, since you didn't post a year or a driveline, I can only guess at this, but - say we're working on a 6.0 diesel, in say...a 2005-ish Super Duty. I believe 03-07 alternator circuits are all the same.

On the top of the alternator, the little 2-wire plug that fires up the alternator field, you should have 12v at the.... holy for the love of god why is my Ford access so slow... Orange/Light Blue wire with the key off. With the key on, you should have 12v at the LG/RD wire on the opposite pin (looking at the face of the connector that goes onto the alternator, the LG/RD should be on the left, and the OG/LB should be on the right, if you're looking at the pin side, the opposite of where the wires come out.)

Like I said originally though, let the truck run for 120 seconds and see if the voltage ramps up after that. Don't see a whole lot of charging system issues other than alternators on Super Duties.


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