That's a *very* good point ! .

I find that most alternator ground problems are caused by dirt/corrosion in the many joints between the alternator proper and the engine block ~ any time you have it apart you should use a steel bristle scratch brush to clean up every place the brackets fit together until they shine .

It's a very simple thing to add *one* brown wire with a ring terminal on each end to the negative battery clamp on one end and the alternator on the other .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Alright folks, I am back with a resolution after some time wrenching today. Here's what I did:

-Measured voltage drop from alt case to negative post on battery. Around -0.2v
-Cleaned the grounds from the battery to the chassis, and from the transmission to the chassis.
-Went for a drive. At idle, power was indeed more stable. But, power was still surging when driving.
-Replaced the voltage regulator.
-Went for a drive, that fixed it completely.
-Just for kicks, redid the first test and the voltage drop had gone UP, to -0.3 volts. No idea why that is.

I suspect I fried my VR when I tried jumping the car a few weeks ago. I did the jumping in the "proper" manner, but, that seems most likely. It should be noted that I had another W123 a while back that I fried the VR on when trying to use it as a donor vehicle to jump another car.

So either these Hella VRs are very sensitive to jumping, or I have bad luck with them. I'll report back if this issue crops up again, but at the very least I won't be jumping this car ever again. Haha.
I will also be adding another ground wire as you all suggested, I think that's a good idea either way.

Thanks for all the responses to my question. This is a great community and I am very grateful to have ya'll in order to keep my lovely old car running nicely.

> Just for kicks, redid the first test and the voltage drop had gone UP, to -0.3 volts. No idea why that is.

If I were a guessing man, and I usually am, I’d say the alternator is putting out more current due to its better connections and regulator. More current equals across same resistance equals more voltage. 0.3 might not be bad if it’s playing catch up with a run down battery.

Michael

0.3 volts drop between alternator and battery is *extremely* good ~ you're allowed .1 volt per physical connection as a loss .

This is why adding a simple ground cable between the battery proper and the engine block makes the charge rate go up and increases cranking speed cold or hot .

I made up a tandem ground cable that goes from the battery to the body on one leg and the intake manifold on the other leg .

Brighter lights too .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Oh ok great. I thought 0.3 was bad. I will be buying some more brown wire today, and going crazy with grounding. Thanks all!