Look for whunter's post #7 in this thread:
http://www.peachparts.com/shopforum/diesel-discussion/323015-no-charge-light-1981-300sd.html?highlight=step

There is a good electrical isolation procedure.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)