2004 F-250 6.0 PSD

i've had some electrical issues periodically but never put my finger on the cause. About 2 months ago i had the batteries tested and the alternator bench tested, everything tested good. Friday i crank up the truck and let it warm up for a few minutes. when i got back in the truck the battery light on the dash was on, which was unusual. my scanguage was showing about 11.5 volts. ficm showing 47 to 48 volts. i put a meter on the alternator wire at idle but it was only showing 12v which was about what the batteries had in them. tried revving the engine and watching the scanguage but the voltage never increased, just fluctuated around 11.5 to 12v.

I fully charged both batteries seperately. Put them back in the truck, battery light comes on with key on and doesn't go off. ran truck for about 4 minutes, battery light still on. voltage at battery posts was 12.22, voltage from alternator post was the same. any fuses related to those 2 wires that plug into the top of the alternator? could something with those 2 wires cause the alternator not to supply voltage? if so how do i check.

i'm guessing that i have a problem with the alternator but any help or direction for troubleshooting would be appreciated.

Thanks!

 

time for a new alt change it soon befor it kills your batts.(if it hasnt allready)

 

i've pulled it out and i'm going to have it tested today. i did some more troubleshooting on it. the green and red wire going to the top of the alternator, apparently it's suppose to have 1 to 3 volts with KOEO and 8 to 9 volts with KOER. This wire from what i understand is what tells the alternator to charge? correct me if i'm wrong.

I have 2.01 volts with KOEO and 2.01 volts with KOER. i checked it several times over the course of 3 or 4 minutes just in case it was waiting on the glow plug relay or whatever. it never changed voltage. i also checked the 3 fuses related to the instrument cluster and all 3 of those fuses were good. what does this mean exactly? does it mean that the alternator isn't being told to charge or that something is wrong with the alternator itself?

 

Attached is the wiring diagram for the single alternator on a 6.0L. As you can see, the Orange w/ Light Blue wire (A circuit) goes directly to the battery through a fusible link, so it should have battery voltage at all times.

The Light Green w/ Red wire (I circuit) goes to the Instrument Cluster. It is what allows the cluster to "turn on" the alternator, and what turns of the battery light if there is a problem with the cluster. On the diesel, the cluster turns on the alternator when the glow plug timer has expired.

The chart below shows what voltage each circuit should have at what times. It is somewhat inaccurate, though, since the I circuit won't be energized until the glow plugs are turned off.

 

thank you, this is the chart that i was going by. with the engine running, the i circuit stays at 2 volts. I dont know if the glow plug timer has expired or not, but i checked it several minutes after i started the truck and the ECT and EOT were around 90 degrees so i'm thinking that the glow plugs should've gone off. what does that mean though? since it's not getting the 8 to 9 volts that it should, does it mean that there's something wrong from the cluster or the alternator?

I took the alternator to oreilly's, they tested it and said that it was bad. it was only putting out 8.5 volts. would that cause that i circuit wire to only keep 2 volts or do i have more than 1 problem?

 

Measure the voltage of the I circuit with it disconnected from the alternator. That would eliminate the alternator from the equation. The glows plugs shouldn't run for more than 2 minutes after the truck starts.

There are 4 fuses that feed the instrument cluster. Check fuses 33, 35, 41 and 45. Also, check the plug for corrosion and move the pigtail around as you check voltage. I have heard of wires breaking off just at the connector causing problems with the I and A circuits.

 

all 4 of those fuses were good. i'm going to take the alternator to a local shop tomorrow and let them look at it. hopefully a new alternator will take care of the problem but if it doesn't i'll check that wire with it disconnected.

 

update: alternator shop said that the alternator had 2 bad diodes, batteries load tested good. Fired it up today, no battery light, voltage went to 13.8 to 14 volts after glow plugs went off. Alternator seems a lot stronger and quicker to full power than it used to be. hope that's a good thing.

 

I've been following your thread, I have an '04, V-10 so far no alt., been told I should expect to replace it, how many miles have you got? I'm at 120,000

 

I've got about 144,000 on mine right now. I've only had it for about a year though so i don't fully know what has been done to it previously. I do know however, that the alternator and the turbo both have a remanufactured sticker on them and the batteries were both bought on january 2010.

 

It seems most modern alternators are good for 100K to 200K. At that point, the brushes are usually pretty much worn down to nubs and start arcing or going completely open.

Any good electrical shop can replace them.

 

A local guy (with an excellent rep from the local shops) rebuilt my original alternator for $80. The diodes are known to crap out, and one of mine had. Voltage regulators are also known to go, and this one was shot (couldn't even hit 13v at full throttle). I think he also put in new bearings and brushes. Ask around and see if there are any shops near you. You can probably get a cheap MIC parts store one for the same price, but its a crap shoot if they'll die in a day or a year.

 

Hey DChamberlain,

New to the forum by the way! How do I test voltage to wires? I know this might seem like a no brainier but what tool do I need and then what is the process? Especially for the wires that are in the 3pin connector coming from the alternator. I think that I have a fusible link or two that is blown from jump starting the truck by touching the starter cable directly to the Red post.

 

I'm having similar issues but with my truck with koeo I get no battery light at all. I've checked voltage from the orange and green wires on alternator and both have 12v on them with truck running. My alternator was tested and is good. My batteries were load tested and were also good I've also replaced the bulb in the cluster twice with no luck. The first time this happened i replaced the bulb in thr xluster and it fixed the issue, then a week later the light stopped coming on again, ive changed my bulbs teice now and thats not the issue. Basically what's happening is when I start my truck the voltage gets lower and lower while idling because without that dummy light functioning in my cluster my truck is telling my alternator not to charge.
So-
-batteries are good
-alternator is good
-i have volts on orange wire coming from battery
-i have volts on green wire going to cluster
-bulb is good inside cluster

but still no light coming on in the dash ever. What s the issue I'm completely stumped. You seem pretty knowledgeable about this so I created a profile on this page to hopefully get a reply from you. Thanks in advance.