1slot jamma harness vs 2+slot mvs harness

I'm looking at hardmvs and wondering what the difference is between the jamma harness on the 1 slot vs the mvs harness on multiple slots. is there a simple adapter available to go from the mvs to jamma?

Your question has me a little confused on what you are asking, but here goes:

A straight up Jamma harness lacks the 4th button for MVS games if all you want is to plug in a single slot Mono MVS board.

A straight up Jamma harness lacks the 4th button, and a select button as well as the Stereo wiring if you want to plug a multi slot MVS board into it.

If that does not answer your question, you can PM or email me.