My friend is visiting from out of state and had a strange thing happen today about an hour from my house. As he was driving, the interior fan suddenly stopped, the windows no longer operated, and the temp gauge, tach and speedo all went dead. He drove it to a nearby Advance Auto and had them check the alternator output - it was around 11.5v. Assuming the alternator had suddenly quit, he purchased the only unit on the shelf and I headed out with a bucket of tools.

We got the 'new' alternator installed without issue, fired the truck up, and saw no change. Thinking one or more of the connections may be dirty, corroded, etc., we did the entire job again only to have the same result. The guy from Advance Auto tested the old alternator and found it was fine when checked on the bench....

The truck is a 1998 SR5, 4WD, 5-speed with 250,000 miles. He's owned the truck since new and has not had any electrical issues to date.

Any thoughts on what may be causing the undercharging? I assume the alternator is looking for a signal voltage to produce a charge.



Andreas

 

At any time was the battery checked ??Battery terminals clean and tight.

Were you checking the output with your own meter ??Clueless counter person ??

I can only guess the charge light was on the whole time.

Poor connection because of corrosion on the alternator plug

open fuse or circuit in the charging system

One of those things you need to check one step at a time

 

- Battery checked fine and terminals clean & tight.

- Output checked by Advance Auto guy.

- No charge light illuminated.

- Alternator plug & three prongs looked factory new (grease still on red o-ring)




Andreas

 

It doesn't seem like the symptoms as described would caused by a poorly charging alt/ bad battery, would they?

 

It's confusing for sure. My understanding is that an alternator needs a signal before it will produce a charge. How the 4Runner alternator receives that signal, or from where, is the mystery.



Andreas

 

That's how it works with people too. They are fine, fine, fine, and then dead, even though they never died before.

What does this mean?

 

The last post in this thread may refer to what I'm trying to explain with a 'signal wire'.



Andreas

 

I was referring to the which systems and how abruptly they were affected, and the lack of affectedness in systems you'd expect.

Signal from voltage regulator?

 

A bit more info: we found that a section of the positive cable was severely hosed (pic below), so we installed a new cable. After doing so, the alternator was showing ~12.3v charging vs. the 11.something we saw last night. So presumably the new & intact cable allowed an additional volt worth of charging...

We checked continuity on all three wires of the alternator harness - they're good (that includes the signal wire). The actual charge wire checks good from the lug on the alternator to where it terminates at the fuse block.

So, the windows are still dead, the tach, temp gauge, and speedo are dead and the alternator still does not push out enough juice.

Thoughts?





Andreas

 

You have gone through and checked all the fuses with a meter ??

Cleaned and inspected all the major grounds where they attach to the vehicle.

The white wire coming off the B terminal of the alternator to the fuse block??

Is it possible to check your alternator output at the B terminal of the alternator

10 Amp gauge fuse Open??

windows pull power from there as well as the alternator !!!

 

All fuses checked with meter.

Cleaned & inspected every ground we've been able to I.D.

White wire is one of three in alternator plug - it checks out.



Andreas

 

Fuses tight in the sockets ??

Yes there is a white wire in the plug But I am talking about the 8 Gauge wire on the stud that goes to the fuse block.

Do I need to make a road trip to help ??

 

Yes, that wire is good.

I'm sure my buddy would take you up on that offer - he's somewhat stranded in MD until we get to the bottom of this.



Andreas

 

Was that positive cable fried/overheated?

Really sounds like some other sort of problem, not the alternator.

Probably time to start pondering a wiring diagram, and working backward from some component that isn't working, junction by junction, to the fuse block. See where the 12V+ stops.

 

That cable had been monkeyed with in the past and started coming apart in our hands.

I agree that the issue is probably not with the alternator. My friend is in somewhat of a time crunch so he's currently at the local dealer to see if they can somehow magically pinpoint the problem.



Andreas

 

Problem solved. A tech at the local Toyota dealer found a 10a fuse that was blown. Supposedly this fuse controlled all of the items that were out of commission. Odd because we checked each fuse...

When the tech reversed the truck to pull it out of the bay, the fuse popped again. So after some more trouble shooting, he found a short somewhere in the trailer wiring.

My buddy is on his way back home now. What a fiasco.



Andreas

 

That makes a lot more sense! Glad the short was found, it's so aggravating when a fuse looks good when it's not. Also glad you posted up too, been wondering what the final verdict would be. Thank goodness it was simpler than it could have been!

 

I told you it was the 10 amp gauge fuse at least it could have been looked at closer.

How does a open fuse check out good??

At least it was fixed

 

No idea. I think my buddy checked that one...

Thanks for all the suggestions - it's appreciated.



Andreas

 

How did you check the fuses? I get tired of telling folks that visual checks are worthless. Either use a test light or substitute a known good fuse.