There are two places to read codes. One of them is at pin 3 of the EZ ignition box, read in duty cycle. The other is the connector near the battery, you read with a diode and a resistor. I made a box many years ago with a resistor, and LED and a pushbutton switch with alligator clips on the leads.

Once I sell my 300E, you can have it for the postage.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution