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PhilSeattle

Quirky Electrical Issue

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I just completed installation and tuning of my newly rebuilt motor. Here’s the background: 74 base model. I re-stroked my 1.8 liter to 2.0L and kept the 1.8 L head. Also kept the 320i distributor and ignition module. This seems like a nice setup and runs like a champ. Huge improvement over what I had... Here’s the issue: occasionally and seemingly completely at random, my electrical light will begin to glow faintly. It doesn’t seem load related- can happen no matter what accessories and lights are on (or off), it can occur at any time and generally sticks around for a little while then magically disappears for no apparent reason. There’s no perceptible effect on engine performance while this is happening. I’m stumped. I’ve checked connections several times, and all looks good. I’ve cleaned every ground I can find.  Alternator(e21) is new and charging system is in good order, though I haven’t metered it while this is actually happening. New alternator belt in place. Any 02/e/21 electrical gurus out there want to take a guess? I’m leaning towards something to do with the ignition module, though I’m using the same module and distributor as before and there was no issue like this previously) Another  possiblility is just that something’s damp? Its been INCREDIBLY wet here in the PNW recently, maybe this will go away if it ever stops raining. I guess I’m not too concerned about this but I’d love to have a clue what’s going on. Thanks all, in advance.

 

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For starters I would monitor the alternator output. You can buy these cheap cigar lighter socket meters that can come in handy. If your voltage warning light is flickering it sounds like low voltage. Be nice to eliminate that possibility.

 

But agreed it's been pretty darn humid in the land of the moss.

DSC_0212.JPG

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A dimly glowing charge light is an indication that there's an imbalance in the voltage between the battery and the charging system.  As I understand it, the charge light has two positive leads--one from the battery, and the other from the charging system.  With the ignition on and the engine not running, the charge light is nice and bright because the battery is providing the current, and there's none from the charging circuit.  When the engine starts running and the alternator is turning fast enough to charge the battery, its voltage cancels out the battery's and the light goes out.  A dim glow while running generally means the current draw is greater than the alternator's output.  

 

Since you say the intermittent dim glow seems to be independent of load (the usual cause) I would start suspecting a loose connection somewhere--didja check the plug on the back of the alternator?  There's supposed to be a wire bail that holds it in place--it's often missing, and a loose plug can cause the intermittent dim light you're experiencing.  Then start checking other connections--the ignition switch, battery cables etc.  The only other thing I can think of that might be causing the problem is a failing alternator or its internal regulator.  They've been known to be defective out of the box.

 

Let us know whatcha find to help expand our knowledge.

 

mike

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Check the ground from the alternator to the block.  Make sure the connection is solid and the wire is not corroded or broken.

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(edited)
1 hour ago, halboyles said:

Check the ground from the alternator to the block.  Make sure the connection is solid and the wire is not corroded or broken.

 

+1  But I would think if you turned on your headlights the dash light would glow brighter.

 

@PhilSeattle

 

As a test, put a second wire from the alt body to the block.  See it there is any change.

 

Edited by PaulTWinterton
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For an E21 alternator, it could also be brushes, voltage regulator or slip rings inside the alternator.

Which would track it being independent of load.

 

I agree, check grounds, check your charge voltage, check the d+ connection to the alternator-

and then don't worry too much.  Especially if you wire in a permanent voltmeter.  Which is always good insurance.

 

t

 

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6 hours ago, TobyB said:

For an E21 alternator, it could also be brushes, voltage regulator or slip rings inside the alternator.

Which would track it being independent of load.

 

I agree, check grounds, check your charge voltage, check the d+ connection to the alternator-

and then don't worry too much.  Especially if you wire in a permanent voltmeter.  Which is always good insurance.

 

t

 

 

BTW, the little digital VM that "7502" depicts looks like the same one I had. Until the reading started dithering downward a volt or 2 on the way to Mid Am 2 years ago. Worst $2.50 I ever spent 😉

 

https://www.amazon.com/Zeltauto-Cigarette-Lighter-Digital-Voltmeter/dp/B00VL9JZ0K/ref=sr_1_2?crid=32Q9LBFFGLFNC&keywords=digital+voltmeter+cigarette+lighter&qid=1581720757&sprefix=digital+volt+meter+cigarette%2Caps%2C194&sr=8-2

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Had a similar issue once.  It was one of the flag pins on the alternator not correctly mating with the plug.  The flag contact was next to, and not inside the contact on the plug - thus intermittent contact.  Unplugged and watched as I mated the connector again to make sure all of the flags were inside the contacts.  YMMV.

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It’s  the variability of this condition that has me most baffled. I’ll follow up over the next week or so and let you know what I find. Thanks all, great responses!

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8 hours ago, 2002 said:

Had a similar issue once.  It was one of the flag pins on the alternator not correctly mating with the plug.  The flag contact was next to, and not inside the contact on the plug - thus intermittent contact.  Unplugged and watched as I mated the connector again to make sure all of the flags were inside the contacts.  YMMV.

I Had the same issue. There is a weird little plug with like 3-4 wires, I had corrosion on them.  Cleaned it up and I was off to the races. 

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I had much the same issue - it was the alternator. But check the wires as suggested above. Is the small brown wire original?

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(edited)
55 minutes ago, Hans said:

Is the small brown wire original?

 

That "small" ground wire is actually supposed to be 4mm² or between 10 and 12 gauge wire.  I like to use something like the one below.

 

And, I just had to post this video-- "That little wire"

Wire Gauge.png

Alternator Ground Strap.jpg

Edited by halboyles
pic

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The dimly glowing charge light is usually cause by a failing diode in the output stage of the alt, in a healthy charging system. Why it is intermittent, who knows. All these other problems described in this thread could conceivably cause that.

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Skin effect or something like that makes it better to use the braided wire for ground straps.

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