Mercedes Benz repair: 1971 250 gas no spark in run mode just when cranking, phone answer, diagnostic data

Question
I have a 1971 250 6 cyl gas auto trans shifter on colum. I have no spark when I return key to run, I loos spark and power to the coil.. ballist risister seem to check ok but i tested it while on the car with wires hooked up  and key off... I have spark and car will start when cranking it in startmode ..this just happend while car sitting in carport... what where and how do i check it is it the key switch? or is their something else to check? car is orig with points coil ect seems with key in run position i should have power to coil but don't..help me please phone  

Answer
Answer:
Here is all the diagnostic data you should need.

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Automotive repair training book on line, you can download it.
http://www.tpub.com/content/construction/14273/