Having trouble with charging system also 85 300 sd
 

I am having trouble with my charging also when running in daytime nothing but radio on according to volt meter inside car I have a slight discharge. I guess the voltage regulator can not be turned up in this alt. I will start checking belt tightness and voltage at battery when running and off. My battery is 5 yrs. old maybe time for a new one. Never had trouble starting yet. Maybe need new alt.

Almost worth throwing a new regulator at it first. You might not have to pull the alternator to replace it but disconnect the battery.

Sixto
98 E320s sedan and wagon

Only an ammeter would show "discharge", but if not >13.5 V when driving, something is amiss. Does the Batt dash bulb light in ACC key before you crank? If not, alt may not boot-up. Many posts.

Well I looked closer today at it seems when not running battery measures 12.6 v and when running even though the volt meter in car reads less then 12 volts at the battery it reads 13.5 so I guess I won't pay any attention to slight discharge on volt meter as long as my battery methods enough juice to keep turning engine over maybe there is something wrong with the metre and I should hook up an amps. gauge instead.

"Not found," at the end of that link.
 

I'd like to read that article but evidently it's been taken down.

Updated link was on post #23 of that thread.

Here it is again:
BOSCH Voltage regulator mod

Oh so maybe I need a new diode in alt. Well never did that and do not know if I am capable of that.

It's not a good idea anyway. The mod was developed for a Pantera, which is a mid engine car with the battery located in the front trunk. The significance of that is that the battery is in a cool area, and a long way from the alternator. The diode circumvents the temperature compensation that's built into the regulator, which is needed because a Mercedes battery is located in the hot engine compartment.

Sounds like your voltmeter is giving strange readings if <12 V across the battery terminals and 13.5 V in the cabin (cigarette lighter?).

Installing an ammeter would not be simple. Some U.S. cars thru the 1970's had that (Chrysler, recall GM dropped in 70's). That required routing thick 12 awg wires to the a dash ammeter and back. When the bulkhead connectors corroded, it often caused plastic to melt. I think a voltmeter is sufficient to know what is going on. You can buy cigarette-lighter ones cheap (HP has one w/ LED's for $6). Good to use on a long trip so you don't get any surprises. Should see >14 V on highway if alternator is working.