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

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