Epson 4500 - Manual (Page 183)

The Interface Boards
FG wire not attached
1. Use the CG screw to attach the round end of the FG (frame ground)
wire to the main board and position the other end as shown.
2. Carefully insert the pins on the optional interface board into the
mating connector on the main board; then secure the board with
the screws provided.
Using the Printer Options
5-45