One step forward.....

Upon finding out about the Overboost clog, I was having much fun driving my 300D when the battery died.

Voltmeter showed that the battery was indeed not being charged.
The dash light didn't come on, but does light with the engine off and the key in the "on" position.

I bought a new alternator and belt figuring there must be a LOT of miles on both. After two days of overnight charging and driving the car to a deep discharge (glad it's not a gasser), I was bringing the new parts home.
As I pulled in the drive, I heard the idle note dip. Sure enough, the old alternator was charging again.

Again, thinking the alternator and belt was about due, I installed them.
Sure enough, close to 14V charging to the depleted battery.

Not for long.

The only time charging returned was when I pulled the plug on the alternator and plugged it back in. That may have been coincidental as charging stopped happening again in minutes.

If wordy posts bother some of you, I apologize but detail and history have always helped me in troubleshooting.

So far I've:

1. Confirmed battery voltage at the field port of the 3 port alternator connector.
2. Found 1V less at the field connector at that terminal block in front of the battery.

I should say that auto electrics are something I'm fond of.
I'd like to know what "X4/10" on the wiring diagram is and I'd like to know how a potential 70A is getting to the battery from the alternator via relatively small wires. There are twin B+ wires at 2.5mm each but still.

Is there a hidden relay somewhere?
Why does the "Battery" light not illuminate while the car is not charging.

Looking forward to your responses.

TIA

Paul

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Albany, NY Suburbs
'87 300D

From you description of what happend when you pulled an re-inserted the Connector on the Alternator it by be a problem in the connector or the wiring to the Connector.

Info from another member:
"ALTERNATOR DIODE check with volt meter
With your meter across the battery, on Volts DC, you should read 12.5 - 14VDC
If not, set your meter to Volts AC and you should have a reading of ~100mVAC.
If the VAC is too high, then look for a rectifying diode failure. If VAC is OK but the VDC is not correct, then the problem is with the voltage regulator."

I have also read on the forum that if one of the Alternator Brushes is worn it will not charg but the No Chargine Light may not come on.

If you like gadgety stuff I made the below Alternator Test Cord for troubleshooting purposes.

Attached Thumbnails

   

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84 300D, 82 Volvo 244Gl Diesel

I'll second the regulator change is needed.
pull it. (two phillips screws) and look it over should have like 10mm of brush length protruding.
if not, or if one brush is shorter than the other, change it out and see if your charging issues are gone!

I like the gadget (and the AC tip).

Given that the same problem occurred with both the old and the rebuilt alternator, I'm inclined to look elsewhere.

I was suspicious of the plug but wiggling it, pulling it off and putting it back on again does nothing. I'm curious about that bock in front of the battery.
Though there is voltage on the field terminal there, it's 1V lower than the other terminals. I've been busy in the yard for the last couple of days so I'll look at it today and report back.

I'll apply battery voltage to the field and ohm out the wiring too.

Weird, lately it's been the little, simple things that have been giving me a run for my money....

__________________
Albany, NY Suburbs
'87 300D

Is your alternator light bulb good? I think that it is required for charging, as a voltage reference to the regulator.

__________________

Gone to the dark side

- Jeff

If there's any short or inadequacy in the Small Wire System (Blue),like say a
connection loose or corroded [Or something Wrong with the Dash Idiot light]
the Alternator will not make any power.
[no "Excitation" circuit]

The X10/4 is just a Positive Transfer Block with Two sides.One for the "Power"
and one for "Signal". The Left side Screw (As you face the Firewall)with the Blue wires is the Alternator "Signal" side of the transfer Block.
The Right side with all the heavy-er cables and Two posts is for Power.
[And Both of the Threaded posts are connected by the plate they are embedded in.]
I've learned from others here that MB's are Plagued with Barely adequate
wire Gauging.

A one Volt loss on such a small cable run is significant.

See gsxr's Alternator upgrade tutorial:
http://www.peachparts.com/shopforum/showthread.php?t=53236&highlight=alternator+upgrade

You'll note he replaces the Tiny Blue signal wire with a larger AWG.

Favorite Alt innards R+Rs:
http://www.oichan.org/mods/alter/alter2.htm
and
http://v12uberalles.com/Alternator_Bearing.htm
(Thank God you've not gotta go through THAT to get to the Alt. !)

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'84 300SD sold
124.128

Thanks all. I SEEM to have sorted it out.

The idiot light works.
It looks like the field path is nothing short of circuitous but I did consistently have juice at the alternator plug.

I disconnected the small wires at the block and spliced in a length of new wire. I connected the other end to the +ve battery post for testing.
The light came on. When I started the car, no charge.

So, I took the regulator off the old alternator and swapped out the new reg.
Viola!

Since I distrust that wild rambling of the field back to fuse 7, I took my new wire there.

The brushes on the regulator are shot so I'll have to replace it.
Are those brushes themselves replaceable? It doesn't look like it at first glance.

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Albany, NY Suburbs
'87 300D

Looks like you may have verified what other members said that the No Charging Lignt may not come on when the Brushes are short.
The FSM has 2mm exposed as being the limit of shortness.

I am not sure where others have bought their brushes but there are Alternator part plasces that sell Brushes so they can be replaced if you can find some.

Peopel say Ace Hardware sells generic type brushes and Carbon Brushes are easy to form to size with Sand Paper on a flat surface.

However, if you have to have 1 set of Brushes sent to you by Mail I doubt if it is as cost effective as buying another Regulator.

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84 300D, 82 Volvo 244Gl Diesel

Thanks.

My wife's taking the rebuilt back to the store.
I guess since I obviously removed the regulator they're under no obligation to me but
who knows? Worth a try.

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Albany, NY Suburbs
'87 300D

... I'd put the new regulator back in the rebuilt alt, and get a new regulator.

Once I hear about whether or not the store will give us another one, I'll figure out what's next. A regulator seems to run about 30 bucks and I can have my old Alternator rebuilt in a couple of hours for about 80.

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Albany, NY Suburbs
'87 300D