could someone please tell me how to get a 420sel to read its codes, the book says there is a relay you can put a fuse into but i cannot find this, there is a cannon plug on left fender but that is all i can find, the car will start and idle but will not accelerate, fuel pressures are right, help!!!!!!

Code retrieve on that chassis is year dependent.............

Codes are real time only, unless a California model.

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E