[TMCopeland]

Not sure what the J9 connector is, but I had Cat hook up to a connector that is just to the left of my driver's seat near the floor inside the cab. I'm assuming you're looking for information on you C15 Cat ? I can send a picture if needed. Then again, I may be not even close to what you're asking LOL

Yes, you are correct, that is the connector.  Newer coaches have a second connector in the engine bay.

Thanks,
Terry