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

[malcolm2]

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.

[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.