cleaning/retensioning connections and belt. Symptom now is:

Light on bright at key on but when alternator begins turning, light remains on about half brilliance. This symptom is temperature sensitive as the warmer the temperature(or engine compartment temp) the more the light extinguishes.
I have a new regulator to be installed later today. If that fixes the trouble, I still will not understand it. Any comments?

Thanks in advance,

ps, where do I go to add my home location to the msg board?

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

you have a voltage drop somewhere in the charging circuit.in a car of this vintage a voltage drop could be caused by high resistance in wiring or corroded connections.i would check that first before major part replacement

Where is the decision made in the circuit to ' send ' electricity to the light ?
On other devices this light might be on the "other side" of something like a zener diode... or resistor, which after 20 years.. is breaking down... an electrolytic capacitor could have dried up or leaked...

leathermang you could be right on this one.there is a diode in the chg light circuit.its located on the back of the instrument cluster.adjacent i assume to the wire for the chg light

Both of my MB's have the charging light " on " low all the time... which I guessed was a faulty setting of the threshold level on the sensing circuit... perhaps they should have had a variable resistor in there instead of a diode... but that diode might just be a one way valve... usually one diode provides a .6 voltage drop in the line....so several normal ones are used together if used for setting thresholds.. but a single Zener can be used backwards in its ' breakover' mode... or something like that... Anyone have a picture of that diode with the color lines showing ? Or a good schematic ?
Yall should not even be reading this stuff... I know nothing about electricity...

ps, where do I go to add my home location to the msg board?

Blue command bar near top of this page, select "User CP" (User Control Panel)
Select "Edit Profile" and fill in

"Additional Information" gives location.

Best Regards
Jim

Why don't you just install an old fashioned Ammeter... ?
That will also tell you if you are over charging for some reason.. and perhaps save you from cooking a battery...

......

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

soon as the diode trio rectifies current from the stator, that voltage is placed on that side of the charge light. The other side of the light is tied ot the battery thru the keyswitch and there is no difference in potential, no current thru the light filament - light goes out....

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

If you are correct that that is the extent of the sensor circuit for the light going on.. then that diode is just a one way switch.. a diode's normal function... I would replace it first since that is easy... because it sounds like it is leaking in the other direction.. not unusual on 20 year old diodes...

self excitation to the rotor when the regulator circuitry senses need for more battery charging.

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

alternator up & checked all nine diodes(all check good). Diode trio diodes are potted into plastic plate that has the connectors to hook up the main rectifier diodes and the wires from the stator. The male connections I thought I had cleaned while the alternator was still on the engine are a mess and looks as tho the only way to get to them to clean them properly is to break things down as I have(or, at least, remove the alternator from it's mount).

Anyone know if the diode assembly is available? I'm going to reassemble my alternator and think it will work after things are cleaned up. I do have a new regulator in case the old one is a no go....

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

I think you should do a little more checking before you start changing things.(IMHO). But your problem does sound like a regulator.

What is your voltage reading across the battery when the engine is idling? (SB 12.5-13.5V) Does it change any when you rev the engine a little? (Maybe loose belts or regulator)If you check voltage with negative to engine and positive to battery, do you get a different reading?(If different, check your grounding Batt.-chassis-engine, I had this bite me once). If you only get a faint glow, especially when warm, the diodes inside the alternator are probably starting to weaken. (Heat is usually the breakdown factor in diodes) What is the condition of the regulator brushes?

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

think the trouble was bad connections. One slip ring(it's associated brush was worn/grooved a bit and shorter than the other one) was grooved. I mentioned, in an earlier post that I had goofed up and installed the regulator/brush assembly upside down. One of the brush connections had pushed against the contact that the brush assembly has to connect to and had compressed it quite a bit, so I think that connection was not quite right also. I believe that the alternator itself was good but I took care of that. I worked on it! I read somewhere that if something wasn't broken - work on it until it was....

Bought a rebuilt alternator from NAPA for $99 bucks. Now - on to the bad crank pulley. Pulled the balancer today. The PO enlarged three of the holes for the pulley and tapped them out(larger) for SAE threads & messed up the other three existing holes. Since we are this far into it, gonna order a new seal but it looks as tho all the oil is coming from the valve cover gasket.. More later, unless someone tells me to shut up....

__________________
Jim

'49 170?(donated to church in Darmstadt '58)
'58 220S(crusher, after '73 fire[San Antonio])
'72 280SE 4.5
'77 240D
'81 300SD
'83 240D parts car

I have the same problem on my '84.

gonna have a look at it tomorow, and may be replace the altenator with one off the parts car that tested good.

__________________
46 WDX Power Wagon

84 300TDT daily driver