I think it's an 87 300E with an 89 300E engine and modified to look like a 95 E320.

That car is neither OBD I nor OBD II compliant and a few posts ago someone mentioned that Sears has on sale for $20 a multimeter with duty cycle function. Exactly what you need to check the EHA function.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD