Red Alternator Light Still On After Rebuild........help
 

I have been going back and forth trying to get to the bottom of this darn RED light on my dash all week.

After I couldn't find anything wrong i decided to get the alternator rebuilt like the forum suggested.

It seemed to be diagnosed as a bad Diode in the alternator and this was leading to the RED light being on 24/7 unless the key was in the run/start position.

Can some one tell me where else to start looking.
I was told by the alternator guys to check the regulator as it was an outboard one.
How do you do this?
Where are all the grounds that I should ckeck?

This is making me nuts. Please help a rookie.

http://forums.pelicanparts.com/porsche-911-technical-forum/341660-alternator-light.html

This is the first thread

More Info:

I Have a brand new battery.
I bought one of those Smart Charger maintainer jobs the other day.

When I hook up my battery terminals and also the maintainer in diagnostic mode.
I can watch the percentage of charge drop while I stand there.
im 10 minutes the voltage drpped from 12.9 to 12.4 snd the percentage of charge to 74%.

There is NO ark when I hook up the terminals.
This drop is like a dead short.
What the H???.

john. i went through this about 6 months ago.
Drove me mad.
ended up pulling the atlernator about 6 times in as many weeks and had it rebuilt 3 times.
in the end i ended up buying a K3 item, got rid of the external voltage reg and havent looked back since.
the K3 item is great.
http://www.k3.com.au/

also sounds like the diode plates are crap. the conections are pressed in and pop out frequently.
you can go down the path of trying to rebuild it but it will be out again in no time

well thats my $0.02c

Hey thanks for the input.

I had the alternator rebuilt today.
I had it done because everyone assumed it was the diodes.

If my VR is bad can it cause the light to come on?

Can start the car for ovious reasons (1:00am).
Will have to try it in the morning and see what it's outputing.

So you had the alternator rebuilt. Did the rebuilder tell you a diode was bad? What did they tell you was wrong?

So you verified that there was continuity from the positive battery clamp all the way to the D+/61 blue wire connection to the voltage regulator. In your PM you say it measured 10 ohms. Close enough for me, considering the bulb filament is in the circuit.

What color was the burned wire coming out of the ignition switch that you heat-shrunk?

What color are BOTH wires going into the bulb holder on the back of the oil pressure gauge? Don't chip the paint on the back of the gauge when you remove it and make sure you disconnect the battery before you do, you don't want an electrial fire.

Did the Tech not recommend to change the external VR to an internal one?
What VR was used for the rebuild/testing?
What was found to be wrong?

They actually delivered it back to my office so I have not talked to the tech.

I will call Monday to talk to the tech.

The wire that was burnt is a 20 AWG White wire on the Key switch.

Can the VR cause the light to be on all the time even with out the key.

How do you explain the huge draw on the battery.

Is it possible to test the alternator if I bring it somewhere and what do they need to do?

Wire On Bulb

"What color are BOTH wires going into the bulb holder on the back of the oil pressure gauge? Don't chip the paint on the back of the gauge when you remove it and make sure you disconnect the battery before you do, you don't want an electrial fire. [/B][/QUOTE] "

The wires out of the bulb holder are:
Blue on one post
RED/BK, RED/BK and BK/RED on the other post.
Three total on that post

Is there away for be to check if the diodes are still bad here?

John,

Questions:
Is there anything can do to the alternator in or out of the car to see if the diodes were fixed?

Is there anything I can do to see if the VR is working properly?
Thanks

Dinner time self serving bump

John:

OK, now we are getting somewhere. Forget about the alternator and the VR for the moment, you need to check the wiring. First, disconnect the battery. This is very important because if a loose wire accidentally shorts you could be in a world of trouble.

Now set your meter to the ohms scale and momentarily connect its two probes together. You should get a reading close to zero ohms, either zero the meter with the adjusting knob or just note what the reading is.

Next: with the alternator out of the car, you should see the small blue wire that goes to the D+/61 terminal on the alternator. Attatch one probe of your multimeter to this terminal. Next, disconnect the blue wire from the bulb holder for the warning lamp. Connect a long piece of wire to this that stretches back to the engine compartment, this is a jumper. Then, to the end of the jumper, connect the other probe of your multimeter. The meter should indicate an open circuit, e.g. infinite ohms, or the opposite end of the scale from when you touched the probes together. Now turn the ignition switch on, the meter should read zero ohms, or pretty close.

What you have just done is verified that you have continuity in the blue wire circuit. If, for whatever reason, the blue wire is shorted to ground somewhere along its run from the bulb holder to the alternator, this test would show it. If the blue wire shorts to ground, the warning light will glow continuously and the alternator won't charge, but only with the key ON. I still believe you had a blown diode problem because you had this condition with the ignition OFF.

OK, so assume you've got continuity in the blue wire. The next step is to verify the wiring to the other terminal of the bulb holder, the one with the red wires with black stripe. So connect one probe of the meter to the positive battery clamp and the other one to the red wire with black stripe. With ignition OFF you should get infinite ohms, an open circuit. With ignition ON you should get zero ohms or nearly so. Now you've verified that the wiring is OK. If some PO connected the wires to an always-hot terminal, this could cause your light to glow continuously even with the key off, but not likely.

Report back on those tests. Do NOT under any circumstances leave the battery connected and try to disconnect the alternator, you can kill yourself by accidentally contacting the battery cable to the chassis or you. ALWAYS disconnect the battery before doing anything.

Thanks everyone for your help on this.
Especially John_cramer who took the time to educate me on how this thing works.

I took the alternator out the next day and showed to my neibour.

He says "Look they didn't fix the diodes, they they are."

Needless to say the shop gpt a call Monday morning and hey had the reworked unit back before 5.

Problem solved. Touch Wood.

I don't know how much is the rebuild. A rebuild unit from Porsche is close to $200. the core charge is is $30. The unit came looking like new. You would not know it's a rebuild unit. A brand one cost $700 from Porsche.

How could the shop not test the diodes? Anybody can do that. After the alternator was rebuilt they should have tested it. I hope they don't rebuild pacemakers.

Anyway, glad it worked out. Good luck!