Car is a 1992 400E. The Check Engine light is on. The engine stumbles when it's warm. I have found a 8 pole diagnostic connector with a button and LED light. This gives me a code 7, which may be "Ignition System Faulty" if I'm looking at the right list of codes. This would be consistent with the performance symptoms.

But next to the 8 pole connector is what appears to be the round 38 pin Diagnostic Connector - I can't be sure because I can't seem to get the cap off of it.

So what's the difference between the 8 pole connector and the 38 pin connector? And what does it take to get the cap off the round one?