Superduty Alternator charging at 20V

[mark]

2005 F550, 6.0 diesel. "New" truck to me. Died on me first time using it, batteries went flat. Had 10V at the batteries. Figured bad alternator so I swapped it out. Still no charge. Traced the wiring to the battery isolator (has auxsilery battery's). It appears I lost one side of the isolator. Checked voltage out of the alt and I had 20 Volts! Changed back to the original alt and it was also putting out 20 Volts. Took both alt to the auto parts store and both checked out with a max voltage of ~15.6.


What do I look at? I'm running out of time, I need to use the truck Wednesday night. I don't know if I have time for the dealer down the street to look at it. I plan on pulling the batt wire for the alt and see what I have without the isolater. Also going to try running a remote ground from the neg term to the alt case and see if that makes a difference.

 

[TreeClimber]

Unhook the second (driver's side) battery and see what happens. (edit; and also unhook any additional batteries, if you have them)

And as a side note... (also owning an 05) the FICM (fuel injection control module) is extremely sensitive to having the correct input voltage. Wouldn't be surprised if it fries.

 

[crash2]

vibration is WAY harder on them thar ficm's

 

[ain'tstuckjustresting]

Also, check for corrosion in both ends of the B+ wire.

 

[mark]

Went to work tonight and dug into it a little more. Reinstalled the new/tested alternator and Completely eliminated the battery isolator from the system. Even connected the original cable from the alt to the batt they had left connected at the batt end but just taped up at the alt end (connections were clean). Now I seem to get no charge. Battery's read same voltage running or not. I did not put an amp meter on them as reading tonight I probably hould have.

I did tear the harness for the alternator connector apart a little, looking for pinched or frayed wire. I can tell this harnes has been messed with. The alternator has a 3-wire connector on it, the harness only has two wires that I found. And orange and a green (both with strips, I don't remember exactly what). The connector has been spliced on, and the center wire has a piece of heat-Shrink on it like it was connected, but I found no mating wire for it in the section of harness I pulled apart (up to the Y were it joins with lots of other wires).

I can't find a good online diagram of what each wire/connector does. I'm starting to wonder if it's even the correct alternator, or should I have a 2-wire connector not a 3. Or do they still use a 3-wire connector, and just use 2 wires.

 

[mark]

Also, I reread what I ordinary typed. I need the truck Tuesday night, as it tomorrow, so I need to get this fixed asap.

 

[Harvester of Sorrow]

Mark,

What ended up being the deal with this thing?

 

[mark]

Battery isolator took a crap. Lost the front charging circuit and aperently on this model truck with this isolator, you run a switched leg to a 4th terminal in the isolator and it somehow tells the alternator to charge, and it must have been messed up and was telling the alter to pump up the juice.

As for the connector on the alternator, the wiring harness on the truck is correct, this model truck only uses a "2-wire" connector on the alternator, but somewhere down the road someone spliced a 3-wire connector in and just didn't use the center wire. Sounds like the two style of alternator wire us the same connector, just one has 3-wires and one only uses 2.

Disconnected the isolator and hooked the charge circuit up as original Ford and everything is now working as it should. Got the night job done with no issues. Really it was just a matter of figuring out how all the aftermarket wiring was configured, what does what, and what has been modified and what hasn't. The way things are routed in this thing will be changed over time, but for now it has a new alternator and new batteries and it good to go. Now to just find some time to have the injectors done before its starts getting too cold and it won't fire.