Ok,

The story is my alternator sometimes charges, sometimes doesn't.
After struggling with it for a few weeks I gave up and went back to the shop where i got my alternator replaced at.
The guys inspected the unit and said my alternator looks to be in great condition. It was putting out 14.4 strong.
I kept telling them about the failure to charge sometimes and suggested a brush problem like a few members of BB have hinted at.
The mechanic told me that if indeed my brushes were worn out, then it would not charge at all, unlike my situation where it eventually does charge.
He told me it would be a waste of $60 labour to yank the entire unit to find nothing wrong and to wait till the whole unit fails and then bring it back to them.
Obviously I don't want to be stranded with a dead alternator in the middle of the night, and the problem seems to be getting worse.

Looking back on the previous repair invoices over the years for this car, I notice that past alternator problems that were fixed by the dealership involved the replacing of a fuse. (This car is a hand me down, and my dad said that the alternator was never replaced, but the dealership did something and the car would charge fine afterwards)

Is there a fuse that I don't know about that could be causing this problem?

In one of my other posts someone suggested a test for the wiring harness for the alternator lead. The red wire that goes from dash to the alternator, is this a wire that needs to be grounded for the light to illuminate? How would I test to see if its grounded? Use a test light or something?

Million thanks.

You might also check the alternator mount bushings (bushes if you are in the UK or colonies)

Sometimes these rubber bushings collapse, allowing the belt to slip under certain conditions

Dear Don:

Chrissij gave you a nice thoughtful response that contains a lot of very useful information that I would follow to a tee. I simply wish to add that your description of "some times charges sometimes doesn't" is a red flag for a loose wire. On my 82 240, (which is notorious for electrical problems from the wiring harness scandal),I had a similar problem and it was due to the fact that I had not tightened the ground wire on the alternator when I replaced it. I hope your solution is as simple as mine was.

Len K

Follow-up to the suggestion is also closely inspect both ends of the ground wire. They can disintegrate internally so that the wires at the heavy-duty eyelet connector for the block or crossmember are only making an intermitent contact.

Onkel Udo

Unlike most electrical failures that are sudden, brushes wear over a long time and when they are near the end of their useful life, they very certainly can be making contact most of the time but not all of the time. The flashing ALT light is a common sign. There are two screws that hold the regulator in place. If the brushes stick out of their holder only 1/8" or so, instead of 7/8", then they are worn and should be replaced. There are other possible reasons for your problem but normal wear or brushes should top the list.

Older 240? Say around 81, or 82? Any later model than that, and I don't think fuses do diddly for that particular problem. Either way,it is a 240, and yes, you should service the fuse panel. If I remember correctly, on the early cars, it's the one for instrument gauges and such, but if this were the problem, I think you would have noticed it. When you turn your key to the number one position, there will be no little red lights across the instrument cluster...

Further, YES, a voltage regulator can cause an intermittent charging problem, it is a "regulator" meaning it regulates for changes in current. Oviously when you are going faster your car is charging more, when you are going slower your car charges less...but yet the alternator puts out a relatively constant voltage...why...because it is regulated by a tiny part with brushes, and a resistor, and circuitry...which can intermittently fail. If all your mechanic is envisioning in his head is the brushes, then he is right. If there were no more brushes, there would be no more charging (though I've seen 'em come in charging with only the left over springs sticking out of the regulator.)

If your car is a B230, with a crank pulley, that could be failing, and basically creating too much drag. Utility bushings could be weak and the belts could be slipping, again...causing a charging problem. I guess we need to know...what year 240, is it the original alternator, how does the wiring look, and if you look down at your belts, while the car is running, are the belts spinning happily and all lined up, or does something look like it's about to wobble off...

Thanks for the replies.

I have a 1980 B21A.
I'll yank the regulator either today or tomorrow and see how the brushes are.

As for grounds, I have a new ground from battery to chassis, and a run of 8 guage from alternator to battery.
Grounds for the engine block seem to be in good condition.
All of these grounds are 6 months old are less. But i'll check regardless.

Thanks for the replies!

You must also have a ground from alternator to engine (usually connects from alternator frame bolt w/8mm nut—to alternator bracket bolt in block). It should be the same size as your output B+ wire (same current flow).

How else can the electrons get back for "revolting" — with the alternator mounted on rubber bushings?
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

All righty.

So I yanked the regulator and checked the brushes, they are fine.
They are a good 1.5 cm and are not worn down.

Ground wires are fine.
Positive wires are fine.
Belt tension is fine.

Now I can only assume is the wiring harness's alternator lead that is at fault.
Any way to test to see if it is at fault?
Does it need to be grounded to light up on the dash?
Thanks

Now I can only assume is the wiring harness's alternator lead that is at fault.
Any way to test to see if it is at fault?
Does it need to be grounded to light up on the dash?

I have sort of a canned reply for these kind of questions, as follows:
>>>>>>
1) The Battery or Not Charging light (and a few more) should come on with Key On.

2) That's due to battery voltage on one side of the bulb(s) and ground (via small red wire to the inert alternator) on the other.

3) With a good alternator, the "Key On" lights go out when the alternator ground path (small red wire) rises to alternator output voltage.

4) With voltage on both sides of the bulb, there's no current flow—and thus no warning light.

5) If the light "glows" when running, the alternator voltage must be dropping below battery voltage.

6) This difference in "potential" allows a small current flow—and thus the glowing light.
>>>>>>>

Take the small red wire off the alternator and connect it to ground. Then turn the Key On. Is the Batt light ON? If so, shake the engine or wiggle wires to see if it goes out or flickers.

If the Batt light doesn't come on, there must be an "open" between the Bulb and 8-pin firewall connector (right side), or between connector and altenator.

Without this Key ON bulb current, the Alternator will NOT even begin to charge. But once it is charging, the wire is just there to light the Batt light if alternator voltage drops (below battery voltage).
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Ok check this out.
If I slam my door shut HARD, the light will illuminate and the thing will start charging.
Its almost comical (to my friends but not me).

Sooooooooooooooooooooooooooo....

I replaced fuse # 13 and no change.
Think its wiring leading to the fuse box or the dash itself?

Sounds like it's inside the car. There are no fuses in the alternator circuits.

The ground for that bulb goes from the instrument cluster (thru the round connector), thru the 8-pin firewall connector, then to the alternator and ground.

Try pulling the cluster and take the round plug off and on a few times. Or separate the 8-pin plug and connect a ground wire (on the instrument panel side) to see if anything changes.

All there is is the bulb-panel plug-wire-firewall plug-wire-alternator-ground wire.


--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.