A few things would help:
Assume serial
Assume D style connectors
In this case, pins or sockets determine male or female
Post a pic of the plotter connector
You can't screw up RS232 in terms of connections. You won't hurt anything if they are connected wrong. Manufactures have made lots of mistakes over the years.
1. Pins or sockets in the connector on the plotter
2. # of pins (could be 9 or 25)
1. Assume 9 pin on the PC, possibly through a USB to serial converter?
2. Probably few things woul a 9 pin male
3. They are eroneously called a DB-9, but they are really DE-9 connectors.
If you know if the plotter is a DTE or DCE device that would be cool.
So, you likely need
DTR
DSR
TXD
RXD
SG
DSR
DTR
PG (protective ground or the shield) - One side only is good
If you can measure the voltage from SG to DSR nd SG to DTR with the plotter on, that should tell us if it's a DTE or DCE.
You likely need a standard serial printer cable to either a 9 pin or 25 pin connector.
The gender used to work
Believe it or not, the wires may actually have numbers written on them. Look carefullly.