Truck overcharging

[Joust]

hi guys.
I'm in a bit of a panic here.
my truck has had the charge light coming on since I bought it. it is intermittent light sorta thing.

today I put my digital multimeter on the lighter socket to monitor the voltage.
when I left home the voltage was 14.25vdc and the charge light was on.
it was like that most of the way to work.
then the lights went off (normal Dash display now) and the voltage jumped to 16.25 and it slowly creeped up and actually touched 18vdc by the time I got to work.
when it touched 18v the abs light flickered on. once I got to work i verified on the battery directly that the voltage was high and it was.
i'm thinking this has to be a problem with the wires that go into the side of the alternator.
I'm looking in the FSM and cannot see where these wires go.
any ideas?
ps
i rebuilt the alternator with new brushes and had it tested. then I put it in with new belts. its working fine. too fine id say....

 

[drmorbius]

hi guys.
I'm in a bit of a panic here.
my truck has had the charge light coming on since I bought it. it is intermittent light sorta thing.

today I put my digital multimeter on the lighter socket to monitor the voltage.
when I left home the voltage was 14.25vdc and the charge light was on.
it was like that most of the way to work.
then the lights went off (normal Dash display now) and the voltage jumped to 16.25 and it slowly creeped up and actually touched 18vdc by the time I got to work.
when it touched 18v the abs light flickered on. once I got to work i verified on the battery directly that the voltage was high and it was.
i'm thinking this has to be a problem with the wires that go into the side of the alternator.
I'm looking in the FSM and cannot see where these wires go.
any ideas?
ps
i rebuilt the alternator with new brushes and had it tested. then I put it in with new belts. its working fine. too fine id say....

It sounds like something didn't get put back together right. I would check the voltage regulator connections inside the alternator.

 

[Joust]

Re: Re: Truck overcharging

It sounds like something didn't get put back together right. I would check the voltage regulator connections inside the alternator.

It would be pretty hard to mess that up. its simple inside. I replaced the entire brush holder with brushes. Then had the alt tested. it tested fine.

 

[drmorbius]

Re: Re: Re: Truck overcharging

It would be pretty hard to mess that up. its simple inside. I replaced the entire brush holder with brushes. Then had the alt tested. it tested fine.

I guess it must be the wiring then. Did you have any problem locating/ buying the brushes? Kind of good to know that you don't have to replace the alternator cause the brushes and bearings are about the only thing that typically wear out. Anyway this is a free bump for you in case anyone has had the exact same problem.

 

[CJ3Flyr]

I would go all over the truck looking for grounds. Every ground I found I'd back the bolt out a turn and then re-tighten the bolt. If the alternator benched 100% ok and it has an internal regulator a ground from the battery to the engine block is the most likely culprit.

If your battery cables and grounds (including the body grounds) are good then try and tie it to heat. Does the voltage act up after the alternator gets heat soaked from the engine? Sometimes the circuit boards/chips in internal regulators (and other components) can get whacky when subjected to sustained heat. It can make for a frustrating diagnosis. Good luck and post what you find
.

:cheers:

 

[Joust]

I'll do that.
wish I knew where all the grounds were.

perhaps its a bad connection on the feedback circuit forcing the output of the alt to go up.
I've ordered a replacement alt just in case.
thanks
i'll reply with my results.

EDIT:
I pushed on all the connectors in teh charging circuit before I started the truck to drive home after work.
the voltage stayed at 4.15 all teh way home and the warning lights stayed on.

I ordered a new Alt.
What concerns me is that when the thing is working properly (outputing 14.25Vdc) the charge and Parking brake lights are on. When the lights go out, the alt is outputting too much voltage. explain that....

 

[CJ3Flyr]

I'll do that.
wish I knew where all the grounds were.

perhaps its a bad connection on the feedback circuit forcing the output of the alt to go up.
I've ordered a replacement alt just in case.
thanks
i'll reply with my results.

EDIT:
I pushed on all the connectors in teh charging circuit before I started the truck to drive home after work.
the voltage stayed at 4.15 all teh way home and the warning lights stayed on.

I ordered a new Alt.
What concerns me is that when the thing is working properly (outputing 14.25Vdc) the charge and Parking brake lights are on. When the lights go out, the alt is outputting too much voltage. explain that....

There should be a ground to the body and the engine that will be fairly easy to find. There's probably more but I'd start there.

If the rectifier is going bad stray A/C voltage will mess up the system. In GM alternators there's a diode trio that can fail and do pretty much what you're describing because the A/C current leaked to regulator confuses it. I don't know if the Toyota alternater uses the same architecture.

Good luck.

:cheers:

 

[Joust]

Well,
I fixed it.
I bought the new Alternator to install if my suspiciouns turned out to be wrong.
but, they were not. I was right. the White "sense" wire going back to the regulator had a knick in it and corroded right through. I put a splice in it and put it all back together with confidence and fired up the truck. It works like a charm.
The regulator was just fine.

 

[CJ3Flyr]

Well,
I fixed it.
I bought the new Alternator to install if my suspiciouns turned out to be wrong.
but, they were not. I was right. the White "sense" wire going back to the regulator had a knick in it and corroded right through. I put a splice in it and put it all back together with confidence and fired up the truck. It works like a charm.
The regulator was just fine.

Sweet! :bigok: Glad to hear you got it...

 

[Joust]

thanks
it was right at the bottom of the wire harness coming from the alternator right at the point that sits on the frame. there is a plastic holder that was meant to prevent this situation. but it actually caused the problem. the edge of the plastic chaffed through the wire insulation and nature did the rest.

 

[My99Runner]

I know this is an old thread, but I have what appears to be the same problem. I have a 99 4Runner and the battery light came on one day. I took it to have the alternator tested, they said it was fine. This was the original alternator with 255K miles on it, I noticed the housing was cracked in multiple places so I opted but buy a rebuilt. I put the new alternator on but the BATT light stayed on, but would go out when I hit bumps. The charging voltage was 14.4V when I tested it upon install, so I figured all was OK. Then after a few days the radio started freaking out, the headlights would get bright/dim depending on RPM's, etc. I measured the voltage at the battery and it was fluctuating between 15 and 19V! I went back to the store and had them test it: regulator bad. So I swapped it out for another one, again the charge voltage was 14.4V but now after driving it for an hour it's up to 15.9V. Battery light is again going on/off on bumps. The battery light comes on when the voltage is normal and goes out when it is high! I have a direct (fused) line from the battery that comes into the cabin for a ham radio so I have a nice way to measure it while on the road. (should have thought of that sooner!)

I'm going to check the white wire as found by Joust and see if that is corroded open.

ETA: The first thing I did was put a new battery in it, the previous battery was all of 7 years old.

 

[Joust]

sounds like something similar.
In my case it was the voltage sense wire that went from the battery back to the alternator. That's pretty easy to check. If the battery is over 14.5V, measure at the alternator. if its high going in there, then the problem is inside the alternator. Simple.

BTW that old truck is still on the road and going strong. rusting itself to death though. its an early 1995 pickup with a 22re.

I will work on it this summer.

 

[My99Runner]

That was it. I removed all of the "protective" stuff from the wiring and there it was, a nick in the white wire that was green with corrosion... the other two were close behind so I trimmed them all a bit, soldered them back together and 'voila', the battery light is now staying off. Looking at the schematic that has to be a voltage feedback/sense wire. When you loose that it thinks the voltage is low so it boosts it up. I was getting fluctuating voltage out of it so this makes sense.

Finding Joust's post made relatively easy work out of this. Prior to digging in, I tested the continuity of the white wire back to the 7.5A fuse and it was open (everything on the fuse block tested fine so I knew it was upstream). My worst fear is that it would be right at the connector on the alternator. Now we'll see how long my repair lasts on that corroded wire! I did get a good solder joint, used that shrink tube with the glue inside and covered in lots of electrical tape. I took a photo or two of the location of the fault if I can figure out how to post it...

 

[Joust]

i'm glad i could help.
That type of heat shrink is the best for that application. it should outlast the truck.

good job.