Here is a pic of the diagnostic scan tool.

You can see in the pic that the LED light needs to be mounted on something. An empty 35 MM film container works fine.

Arthur Dalton deserves credit for the pic, too:

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".