Alternator?

[rockyrunner99]

The low voltage or alternator light came on on me today. The volt gauge however still read pretty much normal. At idle in gear it would be around 12 volts and at a little above idle or more it would be around 14 volts. I have not had the truck very long so I am not used to it quite yet. If there was any difference, it may have taken a few more RPM's to get the volt gauge to go up. Could the light have came on in error, or am I going to be need a new alternator soon? thanks

 

[Skandocious]

Your gauge should not bounce when you change engine RPMs. The first thing I would look at is the voltage regulator. Location depends on the year of the truck. What year and engine?

 

[rockyrunner99]

Oh, it is a 94 with the 300 inline 6.

 

[Skandocious]

On a 94 the regulator should be bolted directly onto the rear of the alternator with 4 screws. Remove those screws (not the inner two) and inspect the brushes on the regulator. You'll see something like this:

The brushes are those 2 black spring-loaded rectangles that are poking out the bottom of the regulator. Check those brushes and see how much life they have left on them-- if you're unsure then try to snap a picture of them and post it here. The brushes in the above picture would be considered bad. When new, those brushes are nearly an inch long.

 

[rockyrunner99]

ok, thanks. I will try to get the regulator off tomorrow to check it out. Do I need to remove the alternator to get the VR off?

 

[Skandocious]

You shouldn't need to. I don't remember the exact configuration of the alternator on the 300 but you should have plenty of room to get at it.

 

[rockyrunner99]

I got mine out, It looks close to the one above, not quite that short but close. I am going to replace it since it is out. It is $20, and I did remove the alternator. I think it was just easier, there was only an in at most to get at one of the screws.

 

[rockyrunner99]

I have the new brushes in now, but did not swap the voltage regulator. It does not seem much different now, but do the brushes take some time to break in and get seated all the way?

 

[Skandocious]

The brushes will definitely take some time to wear down into that crescent shape and get better contact to the stator, but in the meantime the VR should still function just fine. If your problem has not been remedied then you might need to start looking in other places.

How healthy is your battery?

 

[rockyrunner99]

The battery is new (within a year I think) I Think it has to be the voltage regulator, or the alternator itself. Wouldn't the alternator either work or not work with no kinda works. Leading me to think It is the VR.

 

[Skandocious]

Wouldn't the alternator either work or not work with no kinda works.

Not necessarily. There are components in the alternator that can wear down and cause it to produced less and less power over time.

To me it does sound like it's perhaps near the alternator of VR... But the problem with electrical problems like this is that they could be anywhere!

 

[Alvin in AZ]

There are components in the alternator that can wear down...

x2
And those can be replaced and will fix it up good as new, too.

BTDT
The original alternator that came my '75 F150 is still in there
working great, Rockauto and Amazon sells all the parts needed.
But I got mine locally at the bearing shop and Ace Hardware.

Alvin in AZ

 

[rockyrunner99]

ok, new VR and brushes, and still now change, what would you guys suggest next. When I replaced the brushes, I notice one of the contact areas on the shaft had some small grooves in it. I did think much of it.

From the beginning one more time. I have only had the truck about a month so I do not know what normal is really. I had a 91 very similar to it a few years ago. That truck and this one both seemed to struggle when you have the lights and the blower on. Then, on one or two days I really notice the volts dropping when at idle and would be a little lower then normal at RPS as well. I am just quite lost here. All your help is very appreciated.

 

[rockyrunner99]

I might be getting close. I backed up and tried a test I should have started with... unhooking the neg battery cable, and putting a test light between the battery and cable. It came on, showing a short somewhere. It would have to be a pretty big short to cause this problem thought right? I am thinking 5-10 amps or a little more. What could possibly short out like this, it must not be fused!

 

[Alvin in AZ]

I am thinking 5-10 amps or a little more.
What could possibly short out like this{?}

It -could- be fused and -could- be just-enough to light a test light bulb.

Short circuits are the most fun to find.
Opens are way too easy, the meter tells you exactly where it is lickity-split. :/

Anyway, you prob'ly knowed-all that already and this too...
Shorts are found by a process of elimination.

Don't forget the fusible links could be involved and it could be more than one
short so after finding and fixing one short double check the system.

Pull fuses (wherever they are) and fusible links from the starter relay on the
fender well and keep an eye on the test-light while you are at it. One thing
good about it is it seems like it's there to stay so won't clear up on you like
an open from a bad connection tends to do, so you will find it if you don't
give up, it's a certainty, you've got it by the balls now. Even if it feels
like it's the other way around. LOL

Keep posting updates and tell us how you go about it and what you find.

Reading updates are my favorite part.

Alvin in AZ (retired RR signal maintainer)

 

[rockyrunner99]

I hooked the test light up between the neg battery post and the neg battery cable and started pulling fuses one by one. It never went out from the power distribution box under the hood, but when I got inside, there was one fuse, I think it was for the 4 ways, tail lights and some other things. When I pulled it I got the test light to go out. So I hooked the batter cable back up and started it. No difference. So I shut is off and unhooked the battery cable and hooked the test light back up, the light was on when the fuse was still out. I have unhooked many connections around the engine compartment and even the large computer connection and the light stayed on the whole time. I have no idea where to look now, I guess I am just going to keep looking for connections to take apart and check. What about the starter circuit though? I guess I will check that next.

 

[rockyrunner99]

Well I am getting closer, and more frustrated then ever. When I take the power wire off the power distribution center the short is gone, or light goes out. Yet if I remove every relay and every fuse from the PDC one by one, it never goes out. I took the PDC box apart and check the entire inside for shorts and I can not find one. It is clean and corrosion free, and no bare wires. I am stumped.

 

[Mil1ion]

I might be getting close. I backed up and tried a test I should have started with... unhooking the neg battery cable, and putting a test light between the battery and cable.!

The engine better NOT have been running ?

If so,that would be the WORST thing you could do

 

[rockyrunner99]

That test would be pointless with the engine running, why would I do that?

If you have any suggestion as to where the short may be, or an area I should start looking please post that info.

 

[rockyrunner99]

Now I have moved up to the large wire connector that goes through the firewall next to the computer. When I remove that connector, the short it gone. I can not find where that connector leads though, in any of mu manuals or diagrams. Not all the wires there go into the cab do they? I can not believe how much wiring is on this truck!