After the biggest mechanical job of my life (replacing the injector rings and glow plugs) I was putting either the intake or turbo back on when my wrench grounded the wire on the alternator and sparked. The truck had been running a few minutes before with no problems. When I started it again, the alternator light was on.

So my first stop was at the parts store where they tested my alternator, and it was bad. After charging my batteries, I put the new alternator in. All was fine for 50 miles when the voltage dropped.

Advance tested the new alternator and it is fine.

I have replaced the pigtail and the main alternator wire connector.

Checked the batteries and bought a new one.

All battery terminals are clean and tight.

The voltage on the alternator post is the same as the batteries.

Put in a new GPR and tested. My old one was making a clicking noise. Now there is .00 volts coming through when the engine and warm or when the key is off. I will say there is a consistent .022 volts reading on both the smaller posts of the GPR. Is this normal?

I tried disconnecting the fuel heater after the truck starts. That did not help.

I took the pigtail off the alternator, but that did not change things, which I thought was strange.

I tried to have the alternator tested while in the truck, but was told there is a open drain on the battery, even after the key is out, so they could not test it.

Today after taking it for a short spin on charged batteries, I tested both. They were around 11.86 volts. I disconnected one, so I could compare their climb and so the draw would be more noticeable on one battery.

The disconnected one rose steadily to over 12 volts, with the connected one hanging out around 11.96 volts.

Then I took every fuse out, both under the hood and in the cab and noted the volts between each one. I only noticed one effect the reading. When I took number 22 under the hood "Instrument Panel Junction Box", a 50A fuse out, the volts would increase by .01 every time. When I put it back in, it would decrease by .01. Like a switch. Could this be my problem? It seems like an alternator should be able to keep up with that little load?

Is there a list of fuses that can be taken out while the truck is running?

Anyone interested in a free truck?

 

Electrics is not my forte, so no magic for you there. But I do know it is best to change both batteries at the same time, since the weaker will pull down the stronger.

Just to be clear on the problem, it starts and runs, but does not charge?

 

Yes. It will start and run for about 50 miles with the headlights on before it dies.

 

And when it dies are the batteries dead too? If so sounds like the alternator to me.

 

Trace the 2 small wires from the small top plug. The black/orange stripe provides a small amount of juice to the alternator and when that circuit is broken, due to a short or blown fuse, it will send voltage down the green/orange stripe wire which turns your batt light in in the instrument cluster. (The light will come on for other reasons too, but that wire goes to the light.) I went through something similar, and found my black/orange wire was shorting in the valley harness, popping a fuse under the hood, then my truck would slowly die. Without electricity coming to the alt. through the black/orange wire, your alt will not produce a charge. Another thing to check would be continuity between your alt. and your battery ground. Also check your battery connections are clean and tight. If they're not, your alt juice will not get back into the battery. One last thing to check is to see if there's 13-14v coming off the big post on alt while the engines running. These will help narrow it down.

 

there are two fuseable links coming off the fender mounted starter relay. one is for the charging circuit. i bet you blew it when you shorted out the alternator.

 

There is NOT! There is the exact same voltage as the batteries.

 

Today I figured out which link went to the glow plugs. When i disconnected it, there would be not power to the terminal of the GPR.

I then disconnected the other one. The truck would not start with the second one disconnected. Is this a backward way of checking the link? To me, this would mean it is fine. I also checked for resistance between that link and the alternator post and they were connected.

Any other thoughts would be welcome.

 

I took the truck into the store again to have the alternator checked in the truck. It was not charging. In the store it works fine. I think it is clear, there is nothing wrong with the alternator, it is just not being told when to charge.

I tested the two wires coming in on the pigtails. One was a battery voltage reading and the other did not show anything.

Does anyone know where these wires go and what they should be doing?

 

Did you ohm from the big post of the alternator? That should tell you what the alternator is putting out. It should be 14 volts on a good alternator. How did they test it on the truck to say it wasn't charging? And if not why do you think it is good, just because some guy in the store said it is.

 

Ok. I'm not very knowledgeable about electricity, but I ran into this problem in my truck a year ago. I swapped alts. 3 times during a snow storm with no fix. The reason I was having you check voltage on top of the alt is to see if the alt was charging in the truck and voltage was not getting to the batts., or if the alt was not putting out juice. So here's an idiots version (me being the idiot) of how the alt works.
Battery voltage in a small amount flows (not necessarily in this order) through fusible links, then a fuse in the fuse box (under hood on my 01) then through the black with orange stripe to the alt. The alt takes this small amount of juice, which is 12v, somehow multiplies/magnifies it into the same voltage, but more amperage (volume) and sends it back out that big thick cable to the batteries again. The ground for this circuit is the alt. casing itself being bolted to the block. Now, back to the last little wire on the plug next to the black with orange stripe. The last wire is green with either a red or orange stripe. If something goes wrong, and the alt stops charging, electricity is sent through this wire to the dash battery light, telling you there's a problem. You should always have power to the black with orange stripe, as long as the key is turned to on. If you don't, you have a break in it somewhere preventing electricity from flowing to the alt. it could be the fusible links, could be the fuse, or a broken wire. But if that black with orange wire has no juice with key on, that's your problem. Just have to find what's preventing the juice from flowing.

 

with the engine off you should have battery voltage at the large terminal on the alternator.
with key on, you should have battery voltage at one of the small wires on the plug. the other wire on the small plug turns the dash light on.
if you have power to the two wires, you should also have between 13.5 and 14.5 volts at the big terminal on the alternator with the engine running.
if not, there is a problem with the alternator or voltage regulator in the alternator.

 

Yes, I tested the large post on the alternator. It was the same at the batteries. 11.5 volts after I start the truck.

I brought my alternator in the store and they hooked it to a machine that checked all the controls, then spun the alternator. I saw the screen that said it was good. I had them test my old alternator and it failed.

 

Thank you. To make is simple- I do have power to the alternator with the key off, and power to one of the small wires with the key on. I do not have more than 12 volts with it running, so you are telling me it is definitely the alternator. Maybe I will bring it to another store to test it.

 

That's not entirely what he's saying. What color is the small wire that has electricity with the key on? Is your battery dash light on while there's power in that wire?