NOJDOG, on my 84 500SEL US car the green wire hooks to the negative side of the coil and runs up to pin 4 of the diagnostic connector. Being disconnected will have no effect on the engine running.

Start with the basics:

Plugs firing. Check at one of the plugs.
If good
Check for fuel pressure. Not easy on these cars without special gauges.
If good
Check for fuel at the injectors by removing an injector and checking while starting.
if good
Check compression.
If good
Check timing with a timing light
If good
Check for plugged exhaust.

If you make it here, it will run

If you come to a Not Good, let us know and we can try to help.

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84 500 SEL (307,xxx miles)