Hello all! I have used the info on this site to help fix a couple of problems I have had with my 01 F250 PSD, but after reading thru 41 pages of threads , I am out of luck so far and still stumped. Hope someone can help!

My problem is I got in my truck a couple nights ago, started it up, and noticed the battery light on. Immediately checked both battery v's (just changed both batteries less than a month ago)and both were good at 12.5v. So I got home, next morning, checked again, same volt measurements, 12.5 for both. started it up, no problem, getting 12.3 for both. Hmm, Bad alternator? It has 150k on it, and I think original alt, so bring to autozone, they test, same, seeing "No charge". Get home, change alt, exactly SAME condition as prev alt. Plugged my OBD reader in and get NO codes. I read in Haynes that voltage regulator is inside of alt on diesel models? Checked all related fuses according to wiring diagram of charging system for both fuse boxes, and they are all fine.

Basically, batt lite stays on, system doesnt drain power, but doesn't charge either? And no codes on reader. WTH?

I know only very basic stuff about this thing, and learning on the fly, so any help would be appreciated before I take it into the dealership and get ***-raped.
Thanks alot,
Corey

 

First I would replace all the battery cables (if they look suspect)..

Make sure you have a good clean connection for the ground..

Next have the batteries checked under load.. They may be going..

 

I take it that you've already made sure all the battery terminals are clean and all that fun stuff. Yeah, the voltage regulators are internal on these and has been for years. Did Haynes give you the wiring colors and how to probe whether or not the regulator is being fed the proper data?

To make a long story short, when you switch the key on, Power is supplied through the "I" circuit to energize the regulator. That should be a light green wire with a red stripe on it. The regulator measures the voltage on the "A" circuit (Orange with Light Blue Stripe). The regulator then adjusts the output, which goes through the "B+" circuit (Black with Orange Stripe).

It sure looks to me like there are a bunch of fuse links in the B+ and the A circuits. Those are heavy gauge and gray in color according to my book.

Just in case you want to tackle it with a voltmeter, if you connect one lead to ground and probe that harness that goes into the alternator with the key in the ON position, "I" should be 1-3V, and both A and B+ should be at battery voltage. In OFF, only A and B+ should be at battery voltage.

I hope this helps out.

 

Thanks for the responses. I did figure it out after rechecking things, it turned out to be a 5amp fuse (fuse #7,5Amp) inside batt junc box. I thought I had checked through all the fuses using the charging system layout in the Haynes manual, but I must have skipped that one because it is says the one with the fuse is for a dual generator giveaway, and I was thinking that was part of the ambulance package, so must have skipped over that one.

Also, when I was testing, I was getting the batt voltage on the I lead and the B+ lead, nothing on the A lead. Cowboy, you had said the I should be getting the 1-3v, so it had me a bit confused but I did an ohm test and it came back open on the A lead, so I went down the line and found the blown fuse. Replaced it, and the batt lite went out and it is charging at normal rate now.

Just funny how the smallest little things can throw you for such a loop, especially since the haynes manual says that when you get alt symptoms like I had, (lower voltage when running than when eng idle)it says it is most likely defective alt, which is perfectly reasonable.

Ah well, it was a good learning experience none the less.

Thanks again for the input, it got me back on the right track.!!