Gen. 2 Light Flickering

[deumling]

Hi All,

I just had both alternators rebuilt, and after less than an hour of driving, the Gen. 2 light started flickering briefly. I have checked the voltages at the batteries with the engine running - 14.9 on the front battery, 14.7 on the back battery, 29.6 across both batteries. I also tried to check the red and brown wires to the alternators with the key off, and then with key on, per Warthog's instructions, and everything checks out on Alt. 1. On Alt. 2, I check the red wire coming into the white plastic plug with the key off, and it had 12v. There is however no brown exciter wire on Alt. 2. There is just a rubber cap covering that port. I am assuming that is the way it is supposed to be?
Possibly they did not replace the regulator on Alt. 2 when it was rebuilt? The belts are tight and in good shape.

Any suggestions?

Thanks everyone so very much for all of the great wisdom that is so freely shared on this forum.

-ben

 

[Warthog]

Can you post a picture of the Alt2 (GEN2) wiring?

WIth the alternators rebuilt I would say a dirty connection may be the issue. The GEN2 circuit has may connections. More than GEN1. I have the list at work and will post it tomorrow. I may be able to find it in some old threads.

 

[Skinny]

If all your connections check out you may have a bad regulator or other internal piece. I had a very random Gen light flicker after rebuild. I ended up replacing both regulators and the problem never came back. This is assuming everything else is ok...follow Warthog's info first to rule out external problems.

 

[cpf240]

... On Alt. 2, I check the red wire coming into the white plastic plug with the key off, and it had 12v. There is however no brown exciter wire on Alt. 2. There is just a rubber cap covering that port. I am assuming that is the way it is supposed to be? ...

Um, someone correct me if I'm wrong, but as I recall, the red hot wire and the brown exciter wire are in the same plug, so if one is missing, I think that would be a place to start looking. Perhaps the port with the rubber cap you mentioned is the one for the tach output, which is not connected on GEN 2.

Photos of your alt wiring please!

 

[Warthog]

That is why I wanted pictures. I read it same way.

 

[deumling]

Thanks everyone for your quick responses. My stupid mistake. CPF240 is absolutely correct, I was confusing the brown wire with what must be the tach wire. I went back and looked with better light, and there is indeed a red and brown wire going into the white plastic plug, and they both check out per Warthog's instructions. Somehow in the bad light this morning, the second wire looked more blue than brown. My mistake. I am attaching photos of the wiring to the two alternators.

Thanks for the help.

-ben

 

[Warthog]

Remove and clean/adjust the plastic two terminal plug. Many times the connections are loose and dirty. If that doesn't help, you may need to think about replacing the regulator or the rectifier. Even new parts are going bad quickly these days.

 

[Hasdrubal]

I recently had my Alt 2 rebuilt. Gen 2 light is flashing at idle and low throttle settings. Shop is unhelpful, basically brushed me off. So, decided I will take it apart myself and replace regulator, rectifier and diode-trio.

 

[deumling]

Well, I took the alternator to the shop, and they tested everything, and were reluctant to put a new regulator in, as they had just replaced it. They wanted me to conduct more testing on it.

The light only starts flickering once the engine has warmed up/driven for 10 minutes or so. Then it will only flicker when my foot is on the gas. At idle, it will only very rarely light at all.

With the engine running, and throttle up a bit so the light flickers, I have tested the output from Alt. 2 and it stays within 0.25v of 29.75v. I have been driving the truck off and on for a few weeks now with this light issue, and I have not had an issue with the batteries draining, so it seems to be charging okay. I need to drive the truck about 120 miles tomorrow, and am tempted to go for it, but I am worried since the light flickering is obviously an indication of something wrong somewhere.

As I was perusing the wiring diagrams, I noticed that there is a Diode and a Generator #2 Relay in the circuit. Could either of these need to be replaced? If so, where do I find them?

On one last note, the guy at the alternator shop, suggested that I test the voltages coming out of the Red and Brown wires at the white plug, while the light was flickering. Is there a good way to do this? With the plug installed, everything is insulated and I can't find anywhere to access bare wire.

Thanks everyone for all of the help

-ben

 

[Skinny]

My alternators both did the same exact thing, not at the same time but same failure one after another. With a voltmeter directly on the batts, it would spike above 14v when the GEN light flickered. It would occur very quickly, under a second total duration.

 

[deumling]

My alternators both did the same exact thing, not at the same time but same failure one after another. With a voltmeter directly on the batts, it would spike above 14v when the GEN light flickered. It would occur very quickly, under a second total duration.

Did replacing the regulators in the Alternators fix your problem?

I am seeing a slight variation in voltage, but on my digital volt meter, it moves so fast that it is really hard to read. Mostly I just see 29.75v.

 

[Skinny]

I checked directly at the batts, replacing the regulators fixed it.