Thanks for the replies.
@lmtv772, have you used the plug you have as a diagnostic plug? what kind of test kit would you hook up to it? I guess i'm asking are you sure that is a diagnostic plug?
My M1088 is from 1998. The engine was later replaced though; it is from late 2005. Still a 3116 engine, just with a later manufacturing date.
I thought the diagnostic plug (STE/ICE) is the bigger round plug that is on the left side of the steering wheel. I have that too (I guess all MTVs have that)
I went through the STE/ICE test kit manual, and by just looking at all the hookup pictures for each test, I could not find any test procedure that uses that connection.
The cables behind the mysterious 6 pin connector are merged into the main cable assembly, so it's hard to trace where they are going.