Don't know about the M-500, but on my M200E, all the connections from the rear connectors to the main board were identified on the board. 

So you may have luck looking at where the wires attach to the board.

Mike

-------- Original message --------

From: James Smith <js.lanshark@gmail.com>

Date: 11/4/22 6:22 PM (GMT-07:00)

To: greenkeys@mailman.qth.net

Subject: [GreenKeys] INFO-TECH M-500 Manual needed

Does anyone have a copy? Someone gave me an operable(?) unit and cables, but no hookup instructions and every jack on the back of the unit is unlabeled except for a number.

Thanks,

Jim N8AVX