slorider: you might also try posting this Q down in the electrical forum on FTE, since this isn't just a 6.0 issue. I've had some great help from the guys down there, including debugging an alternator issue...

Good luck...

 

Thanks everyone for your help, especially Oz for emailing me the troubleshooting guide. Last night I was able to go through the guide and do all the tests and by their tests it looks like my alternator needs to be replaced once again. I believe there might be an intermittent failure in the internal voltage regulator, although I'm 100% confident that this is the actual problem.

Now a question for the Tech's: I noticed that the guide (414-00-1 Charging System — General Information) didn't have a test for circuit 904, placing a fused jumper wire between generator C102a, pin C, circuit 904 (LG/RD) (circuit that turns on the voltage regulator) and the positive battery terminal. I did not try this for I didn't want to burn anything up, but since the power to circuit 904 is intermittently shutting off wouldn't this test determine that if the alternator voltage never dropped the problem is between the ignition switch and the alternator plug? Or can the voltage regulator simply just short out?

I was thinking about doing the above test because while I had my test light inserted into the top of circuit 904 the test light would go completely out when the alternator would kick off, although sometimes it would just dim very low.... voltage regulator or ignition circuit?

 

So....did a new alt fix the prob? I'm having a similar issue. New batt and new alt from dealer. The day I left the dealer, battery light comes on until the truck gets warm (like ECT 174F), then batt light goes out.

Went through the diag check in 6.0 repair man, all connector voltages check out good. Went back to dealer, they said it was elec prob, and for $68/hr, they'd tinker with it.

Any solutions?

 

BTW, when light is on, volt is 12v, when light is off (after truck is warm), volt is 13.5v.

 

Nope, I've lost track of how many alternators I have replaced over the past 2 years. I've gotten so good at replacing them all it takes is 5 minutes and a 12mm wrench.

When I installed the 4th alternator I also replaced both batteries and was excited after a couple of months that the light hadn't come back on. Although after about 6 months on come the light, once again. I've had to replace the alternator every 6 months or so... it's been 7 months since the last one so I'm sure the light will making its appearance here shortly. I've only replaced it with the parts store lifetime warranty alternator, so I'm not sure if it's an intermittent problem in the truck or just a crappy re-man product?

 

Interesting. My light does not come on at 12V. I drop below that initially. Also, at idle I drop slightly below 13.5V and no light.

 

13mm wrench....?

 

If you can hear the alternator cycling then you have a big load cycling on and off. The only load that big that I know of on the 6.0 is the glow plug relay. Unplug the glow plug relay and see if the problem goes away. You may get a glow plug relay DTC and a CEL but once you plug it back in, the CEL should clear and if you have a code reader you can clear the code.

I thought I read earlier today on another thread that someone had similar problems and the glow plug relay was the problem which is controlled by the PCM. I looked but could not find the thread.

According to my X wiring diagrams the only time the PCM gets involved in alternator operation is if you have dual alternators.

Hope this helps.

DSMMH

 

Snoop23: "Interesting. My light does not come on at 12V. I drop below that initially. Also, at idle I drop slightly below 13.5V and no light"
Let me clarify. Cold: I get a batt light and I'm at 12v. Then, sometime after the truck warms up, I get an instant change: batt light goes out and the voltage jumps from 12v to 13.5v. It does flicker a little while it's "pulling" the batt voltage up. I think the reason the light is on is because the truck is calling for current, but the alternator is not working. Is that right?

 

Sounds like DSMMH has something, I run at 12.8 v on startup, then I ramp up to 13.1 to 13.2 once the glow plug curcuit is turned off. I would look into the relays and the glow plugs them selves. Also, that is a small alt on an SD, especially with lots of electric draws, power this and that, heated seats ect. I would upgrade harness and alt to a 140 if you can. Worth a try, but I think the other link you have to search out is what curcuit is causing this change if its not the glow plug curcuit. You could have another failing relay. Have you done a lot of wiring without using the relays, fuse box, that could have bad connections, worn insulation?