Thanks for all the replies so far. I checked my local MB dealer parts dept for these parts and was pretty surprised that the voltage regulator (pn 0021547206) was $77 and the "preglow time relay switch" (pn 0015459832) is $165 (!) Both were out of stock, so I figured I'd ask if these prices are right for OEM parts, and if any of these can be repaired cheaply; I recall someone replacing a couple capacitors in some part (I don't recall specifics) and saving big $$$'s.
Also, how can I check which part is bad? I charged my battery two days ago, but now I have less than 10 VDC while driving... and a bit more blue smoke while idling than I remember seeing. Also, revving the engine doesn't bring my voltage up at all. Could they both be bad? Could one bad part make the other part fail? Should I avoid driving my car until I resolve this? Strange observation: my tach needle , which hasn't worked in months (years?) began to jump up randomly today...
Robert W. Roe
1983 300SD 264K mi