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Discussion Starter #1
I'm getting about 12.5 at idle and 13.5 above 2000. I would have expected high 13s at idle and 14.4-ish above idle.

I always thought a typical alternator should put out around 14.4 volts when the rpms come off of idle. Most all car audio specs for amplifiers are based upon 14.4 volts since that is the typical output...supposedly.

Got the car running yesterday...basically for the first time...after a while I noticed a red glow on the tach...so I hook up a voltmeter to the car. 12.5v at idle and 13.5 if I rev it up past 2000.

1978 Spider. But based upon various PO notes, receipts and searches of AflaBB posts by the PO...I believe the alternator on my car is an 80 amp unit for a 92-94 Spider.

I've heard that some alternators can be adjusted. Not sure if that applies to Alfas, or what year Alfas...

Or is this possibly a bad diode or failing internal regulator?
 

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But Mad North-Northwest
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Bosch voltage regulators are generally set to 13.7V, I believe. That's measuring directly at the alternator lug: if you use the internal gauge it includes voltage drop through the wires and across the ignition switch, which can be significant.
 

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Discussion Starter #3
I hooked my voltmeter to the fender block where the alternator connects to. That's pretty close to ground zero. So I guess mine is working well enough?
 

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after a while I noticed a red glow on the tach...so I hook up a voltmeter to the car. 12.5v at idle and 13.5 if I rev it up past 2000.
As Gubi wrote, your voltage levels sound OK. But tell us more about that red glow on the tach - does it keep glowing at idle?

If your car has an 80 amp unit for a 92-94 Spider then its brush/regulator looks like the photo below. These are inexpensive (~$20), easy to install and replacing them can cure a lot of ills. I even see that the one below is labeled "14V".

 

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But Mad North-Northwest
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Well the revving value seems about right but it seems low at idle. But I haven't measured my cars in a while so don't recall how much it'll drop at idle. If the alternator is borderline it's possible you could be seeing too low a voltage.

Also make sure your battery is fully charged when you do the tests.
 

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its a bit low if you ask me
at 1500 rpm I'd expect 13.8V to 14.4V (measured across the battery itself)

if you have an alt with the inbuilt regulator (sounds like you do, as you say its from an S4), you should check the brushes...they should be even and not too worn down low (2 screws and the regulator comes off the back of the alt. with the brushes unit complete.
Also see the regulator in Jay's photo above...you'll notice one of the screw holes is metal...that is your ground...make sure that is clean, as well as all the other connections on the Alt

the 'adjustable alt' you speak of, is in fact an adjustable regulator.....from a volvo guy...whether he is still active, dunno...info here from a few years ago:
Battery draw on my 91 Spider Veloce
 

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1978 Spider
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Discussion Starter #7
red glow was the gen light on the tach...I just figured everyone would make that connection...my bad for not being specific.

i noticed the light one after it had been idling a while and I was checking other stuff out. a quick blip of the throttle and it was gone and did not return. I would not have expected it at all if the idle was at spec.

but my tach i'm not sure of. when shut off the tach needle is stuck at 1000. I know it's cable driven but I would expect it to drop to zero. It probably needs lubing. a light machine oil? I suspect the speedo could use the same.

this car will be having numerous little issues as I sort thru it.
 

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Discussion Starter #8
The adjustable reg looks interesting...will have to remember that once a have a reasonably well operating spider and start looking at "improvements"
 

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but my tach i'm not sure of. when shut off the tach needle is stuck at 1000. I know it's cable driven but I would expect it to drop to zero. It probably needs lubing. a light machine oil? I suspect the speedo could use the same.
Is it actually stuck at 1000 or a bit below (600ish)? There's a little post that prevents the needle from going clear to zero.
 

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red glow was the gen light on the tach...I just figured everyone would make that connection...my bad for not being specific.
I knew what you were referring to - just wanted to understand the circumstances that caused it to glow, which you did explain as:

i noticed the light one after it had been idling a while and I was checking other stuff out. a quick blip of the throttle and it was gone and did not return.
That can be a symptom that the brush-regulator assembly needs changing.
 

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Discussion Starter #11
a quick pic of the rear of the alternator. Appears to have that regulator bolted to the back. So guess it is an S4 alternator?

Sorry GV27...forgot to check the tach when at rest and record what I saw (will do that this weekend). I think it hangs up at different settings...didn't know about the needle post. I just figured all tachs would/should drop to zero.

Didn't have the opportunity last night to pull it off (will do so this weekend) or poke around more...busy learning new swear words while trying to remove the oil sending unit...cashing multiple issues on my new project/basket case...
 

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odd looking old fashioned regulator, I have seen them like that on old units, but normally the bosch regulator looks like that shown above in Jay's post (#4)
I'd remove it and see the condition of the brushes.

The oil sending unit requires a quite "thin" wrench to fit between sender and engine (an old cycle wrench would work).....go in from the front, once you have cracked it open, it spins off by hand
(some are 14mm some are 17mm)
 

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Discussion Starter #13
I think that's a cover over the regulator. or a protective cap? will remove this weekend to inspect.

got the sender off with a stubby 14mm...got that going in another thread actually :)
 

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odd looking old fashioned regulator, I have seen them like that on old units, but normally the bosch regulator looks like that shown above in Jay's post (#4)
A number of different companies make these things, and externally, they may look different. I assume their electrical values differ based on the model of alternator, so bring your alternator p/n and the old unit to the parts counter when you get one. Your local NAPA store probably stocks them, but the ones that they carry may look different.
 

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Is it actually stuck at 1000 or a bit below (600ish)? There's a little post that prevents the needle from going clear to zero.
Both tach and speedo are sitting on those tiny posts...I never new they existed...solves my tach & speedo mystery :)
 

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this is what I pulled off the alternator. One of the brushes look more worn down that the other. not sure how big a deal that is so lone as it makes good contact.
It is normal for one brush to be more worn than the other - I can't explain why. The difference between your two doesn't seem that great. That that regulator-brush assembly may have electrical issues that aren't readily visible, such as a failed diode.

Keep in mind as well that we're "shooting in the dark" here - I never said "your symptoms will certainly be fixed by replacing the regulator-brush assembly"; just suggested that since they're cheap and easy to swap out, why not give it a try.

Was looking at Vicks...they list an adjustable reg. Looks like it should fit any late Bosch type alternator. Any one using the Vicks unit?
I'm not getting what the benefit of an adjustable regulator would be. Thousands of vehicles roll off the production line with conventional regulators and seem to work OK.
 

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Discussion Starter #19
A blown diode has definitely come to mind...I recently reversed my battery terminals "accidentally" for a couple seconds (a PO installed a battery with reversed terminals and I was careless)..which did result in both fuel pumps getting fried. Unfortunately I do not have any voltage readings prior to that to compare to.

The adjustable benefit would be that you could fine tune it if needed. Obviously that's not going to compensate for a bad diode. I think there are a few diodes typically in the VR. Losing one will drop some voltage but not completely kill the alternator I think, but it's effectively no longer functional to maintain battery charge and handle electrical loads.
 

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this is what I pulled off the alternator. One of the brushes look more worn down that the other. not sure how big a deal that is so lone as it makes good contact.

Was looking at Vicks...they list an adjustable reg. Looks like it should fit any late Bosch type alternator. Adjustable Voltage Regulator, Alf Spider, Milano - (SKU 20-8804) [20-8804] - $25.95 : Vick Autosports, The Premier Fiat and Alfa Parts Source

Any one using the Vicks unit?
Unevenly worn brushes do mean something, imo...
(not yet in your case as they are only slightly different)
But I would change that regulator anyway, it looks like something fred flintstone might use.
Personally if I have a Bosch unit I put Bosch parts back in it...especially electric stuff (think Dizzy)

When they are very worn, stick your finger in the hole and feel the commutator for wear or any slight roughness/grooves on the commutator
you might find it has worn more on the 'one half' or is worn rough...if so the alt needs refurb.....just putting new brushes is a band aid.
this is real uneven wear, it is not normal and there is always a reason.
worn brushes.jpg
and usually when you look at the commutator you see something like this
(this is not one of our Alts, but illustrates unevenly worn slip rings well...look at the right hand side, there is a much deeper wear groove)
worn commutator.jpg
 
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