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Old 03-20-2006, 04:47 PM
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alternator wire hanging in mid air?!

I have had an issue whereby I dont think I am getting a charge from the alternator. I had another thread started, see below.

voltage keeeps slipping off the scale at idle.

I had kind of put it on the back burner whilst doing a couple of other jobs as the car is only used during the day time so it doesnt really suffer. It is low revs and use of lights that really kills it.

Anyway, tidying the wiring in the engine bay I decided to trace the wires on the alternator to find the field wire to use for my electric choke installation.

I found that the alternator is fed with two wires, (red and white) see photo. You have to at least give me points for the alternator collage!

Anyway, the red wire comes from the battery feed onto the connector block and from there to the stud on the back of the alternator. it brings 12V to the alternator.

The white wire connects to the other pin inside the connector and heads towards the back of the car?! Onto the floor and trace the wire...it ends up in the trunk (battery is in the trunk) with a large eye ring on the end of it that LOOKS like it is the same size as the bolt used on the +ve connector of the battery.

Now it seems to me that means it should be connected to the positive terminal of the battery and someone simply forgot to attach it when they replaced the battery?

Any thoughts on what it should connect to?

FYI, when the engine is running I have 12V (actually more like 11.3V as the battery is now low) on the red wire and 0.3V (?!) on the white wire which it is obviously getting from the alternator as the other is swinging in mid air!

So, is the alternator fried or is the levitating white wire the problem and if so what should I connect it to?

As always, thanks!

Paul
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Old 03-20-2006, 05:21 PM
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Doc here,

That white wire SHOULD go to the idiot lamp, or volt gauge, then to a resistor (bypassing the lamp) and onto a fuse to the Ignition.



In a stock GM , It's a brown wire...

Ignore the 3 Rd red wire in the diagram unless it's an 81 only GM.

In your case, I think you can hook it up to a SWITCHED battery source, (equal to the brown wire in the diagram, to bypass the lamp/fuse in case they open) and it should charge.

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Old 03-20-2006, 05:45 PM
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hmmm...I have connected the white directly to the battery as a short term fix to see if it would charge.

No such luck. The voltage measured at the alternator (red) was down around 11.3 and continuing to drop, identical reading at the battery +ve terminal.

Does the fact that I only had 0.3V on the white wire maybe indicate that the alternator has an issue? I would have expected that if this were the wire feeding a charge back to the battery it would be more like 14V?

Could the fact that the engine was run for the last month or so with the white wire disconnected cause a problem on the alternator?

Paul
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Old 03-20-2006, 06:08 PM
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Doc here,

I would say, the Alternator is probably flat..

Pull it and take it to auto zombie and have it tested..(or your local parts house), should be a freebie..

Either the regulator is not turning on, or the rectifier diode pack is open, both are replaceable if you want to get a kit..Or you can just get a new one.

I don't think wiring was an issue, It might have just been it's time to go..

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Old 03-20-2006, 06:29 PM
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blimey, you make it sound like a family pet, "might have just been its time to go" !

Thanks for the help. I will likely replace the unit as a whole. Hopefully I will then see a healthy 14V output.

...so if the white wire was NOT the issue what purpose does that wire in fact serve? If it feeds the idiot light from the alternator why does it then go on to the battery via a fuse?

I will run it as per your diagram above from the alternator to a switched supply although I am curious as to what it does if it has been disconneected for so long without causing an issue?

And for my other thread on the electirc choke which of these wires is the field wire to which I should feed the electric choke relay, the white one?

thanks,
Paul
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Old 03-20-2006, 07:00 PM
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Doc here,

The white wire is what you need to deal with..

If you don't want a lamp you can just wire it to switched 12 volts..

It's function is to excite the regulator in order for it to Charge..

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Old 03-20-2006, 07:06 PM
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Thanks doc, I got it.

Once up and running is this white wire the wire to feed the choke relay from?

Paul
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Old 03-21-2006, 02:33 AM
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Doc here,

Yup, you got it.

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Old 03-21-2006, 04:20 AM
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"The white wire is what you need to deal with..
It's function is to excite the regulator in order for it to Charge.."
So if the white wire was hanging loose that could the reason he was´nt getting charged.If he connects up correctly there would be no need for a new alternator.
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Old 03-21-2006, 07:21 AM
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Thanks malc, Doc did suggest that by hooking up the white wire I should be fine but when I tried it I had no luck. He then said that maybe the alternator was 'flat'.

I will be replacing the alternator AND then hooking up the white wire to a fused and switched supply.

HOWEVER...the wire that that primes the choke relay is, to my understanding, only to have a 12V supply when the engine is running. That is the reason to use the field wire from the alternator. The white wire will, being fused direcly to a switched supply, have 12V when ever the ignition is turned on instead of when the engine is running??
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Old 03-21-2006, 08:55 AM
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I brought the alternator to the local NAPA store where they informed me "it didnt start, it didnt get excited". They said it was probably the regulator. So, I bought a complete new unit and installed it. I now get 13.8V on the white wire when the engine is running!

I have the white wire connected to the fused, switched supply as well.

Thanks for the all the input!!!!
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Old 03-21-2006, 02:47 PM
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Doc here,



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