ALT light troubleshooting. FIXED, Specifically, what makes it come on? Options

[malcolm2]

You can test the alternator by removing the VR and shorting D+ to DF. This is equivalent to the VR providing maximum drive current to the rotor magnet. With the car running, the alternator should generate more than 16V. If the alternator doesn't provide >16V and the GEN light stays on, likely the alternator needs replaced.

To be clear,

I remove the VR.

Use a short wire to connect the D+ to the DF female connections on the relay board now visible from removing the VR.

Which should be the 2 that are side by side (or the btm of the triangle formed by the 3 connectors)

VOM on + & - of the battery.
start the car.
read the meter.

So if the ALT gives me >16 volts I can assume I need a VR?

Correct, the 2 side by side spades.

Correct on the procedure. What you are doing in effect is fooling the alternator to appear like the VR is trying to maintain maximum charging/voltage output.

If you do get 16+ volts the alternator is able to charge the battery. Even 14+ volts would be good considering if your battery is deeply discharged from not having a functioning electrical charging system.

TADA.... good test results here.... (IMG:style_emoticons/default/aktion035.gif) Well, maybe not GOOD, but at least now I got an expected result. With the VR out and the DF and D+ jumpered, my VOM reading at idle was 0.3 (12.3) higher than with everything connected.

Then I rev'd her up and the reading was 16.1 volts. (IMG:style_emoticons/default/bootyshake.gif)

So the result here is telling me that the ALT is doing it's job and the VR is over doing it's job by shutting the voltage down going to the battery and it will not charge.

So what VR to buy? (IMG:style_emoticons/default/shades.gif)

[Spoke]

Definitely a good sign. It shows the alternator can charge the battery. Gotta make sure the diodes in the VR circuit are ok.

Did the GEN light go off?

[malcolm2]

Definitely a good sign. It shows the alternator can charge the battery. Gotta make sure the diodes in the VR circuit are ok.

Did the GEN light go off?

with the jumper attached,

I start the engine.

It idles at 800 rpm, VOM is reading 12.5 and the light is on.

Rev the engine to 2500, VOM raises to 12.8 the light dims,

Rev to 3000 vom raises to 17 and the light goes out

Return to 800 and the light stays out.

In the past, once I started the car the G light went out and stayed out.

[Spoke]

The alternator seems to be at least providing voltage. Based on your resistance measurements from DF to D+, I'm not sure you're out of the water wrt the alternator.

When you get a moment, retest the resistance measurement from DF to D-. Measure in both directions (Pos on DF, then Pos on D-). Both should indicate open circuit.

[malcolm2]

The alternator seems to be at least providing voltage. Based on your resistance measurements from DF to D+, I'm not sure you're out of the water wrt the alternator.

When you get a moment, retest the resistance measurement from DF to D-. Measure in both directions (Pos on DF, then Pos on D-). Both should indicate open circuit.

Do you mean the female connectors on the ALT harness, or the male connectors on the VR.

I did the VR connectors and saw no difference (still over 80 ohms) when swapping the red and black leads. Post #20

[worn]

I noticed the last time i parked that the red "G" light had come on slightly. Got in yesterday and it was on bright and the volt meter was at 10.5. Revving the engine did not help either.

I checked the belt tension and decided to tighten it.

Took a 20 minute drive to Nashville and all was well. At the last stop i saw the dim G light again. Then bright for a while. Then out.

What is the prognosis? I have about 20k miles on the alt wire harness and gel battery. Maybe 10k on the rebuilt alt.

Try:
http://www.pelicanparts.com/techarticles/9...roubleshoot.htm
works well even if it is troubleshooting.

[malcolm2]

Try:
http://www.pelicanparts.com/techarticles/9...roubleshoot.htm
works well even if it is troubleshooting.

the following is the TS part of your link:

To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.

To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere. If it doesn't, then the alternator is almost certainly bad...

Paragraph 2 is what SPOKE suggested and it gave me >16 volts at the battery, but did not put the light out until the output was > 13 volts. But then the light stayed out at all RPMs.

My question is para #1. I don't follow what to do, how to test and measure. It says to put 12v on the relay board DF. I can do that BUT:

is the car running?

am I measuring volts at the battery?

Should the light go out?

[worn]

Try:
http://www.pelicanparts.com/techarticles/9...roubleshoot.htm
works well even if it is troubleshooting.

the following is the TS part of your link:

To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.

To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere. If it doesn't, then the alternator is almost certainly bad...

Paragraph 2 is what SPOKE suggested and it gave me >16 volts at the battery, but did not put the light out until the output was > 13 volts. But then the light stayed out at all RPMs.

My question is para #1. I don't follow what to do, how to test and measure. It says to put 12v on the relay board DF. I can do that BUT:

is the car running?

am I measuring volts at the battery?

Should the light go out?

The light will originally allow current to flow from the battery thru the light into the alternator windings. This produces the necessary bootstrapagnetic field to start generating electricity. Eventually the voltage generated will match or slightly exceed the battery, so the light goes out. Should go out. You cannot make alternator power without at least two watts of bootstrap power thru that light bulb. Woe be to the person who tries an LED.

[Spoke]

The alternator seems to be at least providing voltage. Based on your resistance measurements from DF to D+, I'm not sure you're out of the water wrt the alternator.

When you get a moment, retest the resistance measurement from DF to D-. Measure in both directions (Pos on DF, then Pos on D-). Both should indicate open circuit.

Do you mean the female connectors on the ALT harness, or the male connectors on the VR.

I did the VR connectors and saw no difference (still over 80 ohms) when swapping the red and black leads. Post #20

I meant measure towards the alternator. Trying to see if the diodes in the secondary (DF, D-) are ok.

[Spoke]

Paragraph 2 is what SPOKE suggested and it gave me >16 volts at the battery, but did not put the light out until the output was > 13 volts. But then the light stayed out at all RPMs.

My question is para #1. I don't follow what to do, how to test and measure. It says to put 12v on the relay board DF. I can do that BUT:

is the car running?

am I measuring volts at the battery?

Should the light go out?

Yes you should be measuring at the battery; you're basically measuring the primary side of the alternator.

How many times have you repeated the DF/D+ shorting test? Do you get the same results each time? You can let the car run for a couple of minutes to charge the battery while you're there.

Paragraph 1 is the same test you're doing except the the power to D+ is from the primary side of the alternator connected to the battery.

The test you've done tests the ability of the alternator secondary voltage to power the alternator with the VR.

One other test to do when you have DF/D+ shorted: Measure the voltage from DF to chassis ground and battery to chassis ground. I want to see if the secondary is producing the correct voltage. The 2 voltages should be very close to each other.

[malcolm2]

How many times have you repeated the DF/D+ shorting test? Do you get the same results each time? You can let the car run for a couple of minutes to charge the battery while you're there.

One other test to do when you have DF/D+ shorted: Measure the voltage from DF to chassis ground and battery to chassis ground. I want to see if the secondary is producing the correct voltage. The 2 voltages should be very close to each other.

I have done the shorting test 2 times, yes I get the same results each time.

VR out, jumped DF/D+
key on, light on
car start, light on, battery 12.3-ish at 800 rpm
2500 rpm, light dimming, battery at 12.5-ish
3000 rpm, light out, battery at >16
back to idle and the light stay out, battery at 13-ish.

I left the VOM on the battery for the last few days. After I did the last test the reading was 12.53v, this morning it was 12.43 volts. So I would say the battery is almost fully charged, correct?

I'll try your "other" test this afternoon. BTW, I bought a new VR to have, incase that is the final verdict. went with the cheaper German one, BEUR.

Thanks so much,

Clark

[Spoke]

How many times have you repeated the DF/D+ shorting test? Do you get the same results each time? You can let the car run for a couple of minutes to charge the battery while you're there.

One other test to do when you have DF/D+ shorted: Measure the voltage from DF to chassis ground and battery to chassis ground. I want to see if the secondary is producing the correct voltage. The 2 voltages should be very close to each other.

I have done the shorting test 2 times, yes I get the same results each time.

VR out, jumped DF/D+
key on, light on
car start, light on, battery 12.3-ish at 800 rpm
2500 rpm, light dimming, battery at 12.5-ish
3000 rpm, light out, battery at >16
back to idle and the light stay out, battery at 13-ish.

I left the VOM on the battery for the last few days. After I did the last test the reading was 12.53v, this morning it was 12.43 volts. So I would say the battery is almost fully charged, correct?

I'll try your "other" test this afternoon. BTW, I bought a new VR to have, incase that is the final verdict. went with the cheaper German one, BEUR.

Thanks so much,

Clark

The battery voltage looks ok. Battery voltage when sitting should be around 12.6V.

When running, after first start up like you described, how does the voltage increase with RPM? The first startup you describe seems it takes a lot of RPM to get to 16V. It could be for the first rev up the battery is charging heavily and taking voltage slowly. This is why subsequent revs may show better how the alternator output voltage changes with RPM.

BTW, did you try the new VR? If the alternator is ok, installing the VR should bring your charging system back to service.

[malcolm2]

Heading home now. FedEx said they are should be there today. I'll do more tests maybe take a video within the hour.

[malcolm2]

well damn, I did the D+/DF short test once more and I got no result. 3rd time is not the charm. (IMG:style_emoticons/default/piratenanner.gif)

VOM stayed on 11.9v regardless of the rpm. light stayed on, of course.

Not what I was expecting.

[malcolm2]

Cancel that post.... 4th time I got the light to go out and >16 volts.

I tried your "other" test and got the following with DF/ D+ shorted:
1st time
DF to frame 2.5
Batt + to frame 12.99

2nd time
DF/frame crazy numbers... jumped to max, I changed the scale and got over 100?

still 12.99 batt to frame.

Maybe I screwed that up. not going well today.

I'll give it all another shot from the start.

EDIT: I must truly have an intermittent problem. Each time I do the DF/D+ short test I get alternating results.... 1 time I get >16v and the light goes out, next time I get 11.99v and the light stays on.

same for the "other" test DF to frame = 2.5 if the light is on and crazy # if the light is off.

I turn the car off between the tests, then restart. And I do not touch the jumper or the VOM leads.... just the key.

[ClayPerrine]

Sounds like something in the alternator wiring. I would get online and order a replacement harness. One of our illustrious vendors makes new ones. But to put it on, means removing the alternator, so just get a new one of those too.....

[Spoke]

Sounds like something in the alternator wiring. I would get online and order a replacement harness. One of our illustrious vendors makes new ones. But to put it on, means removing the alternator, so just get a new one of those too.....

Check the trans ground strap while you're at it.

[malcolm2]

Sounds like something in the alternator wiring. I would get online and order a replacement harness. One of our illustrious vendors makes new ones. But to put it on, means removing the alternator, so just get a new one of those too.....

I guess I'll pull the ALT. It has been rebuilt once and fixed once. The shaft was moving in and out making a clunking noise. I took it back and they fixed it with no 2nd guarantees (IMG:style_emoticons/default/blink.gif) That might have been last summer.

Are there new ALTs available? I think I rebuilt this one, cause I had a hard time finding the exact one we need for a 914.

Anyway, I'll get it out and check continuity on the wires. That harness is from Jeff and has about 20K miles on it.

Is there a chance that the relay board has issues?

The system is the ALT, the VR, the ALT harness and the relay board, right?

[malcolm2]

The bitch is out. I rang out all 4 wires and they all had continuity.

Is there a shade tree test for these fuching diodes? Or should i just take it in and say "sumpin' is fuched up, please fix it!"

[Spoke]

I have tested diodes on an alternator but you have to take it somewhat apart to get both ends of the diodes.

You may be best off getting a rebuilt alternator and start from scratch.